"world news" with diane sawyer. good evening. we begin with breaking news on the massive earthquake hours ago in mexico. here is the moment it struck in mexico city, frightened workers frieding out the quake. one person said we didn't know whether to run or fall on the floor. out on the streets, mothers comforted their children until the quake passed. it seemed forever as a highway bridge was no match for the quake. a car was pulverized. the epicenter of the quake was 115 miles outside the beach resort of acapulco and thousands of american travelers are in the quake zone there. one of them, the president's oldest daughter and the white house weighed in on that today. as abc's david wright tells us about the moment of impact. >> reporter: the powerful quake hit around noon local time. a violent shaking motion. >> horrible, horrible. >> reporter: people felt it all the way to mexico city. abc's jose cohen is there. >> as you can see, people are afraid to go back in -- afraid of replicas. >> reporter: several bridges collapsed there. one truck was crushed. but so far, there've been no reports of death. many people captured the frightening scene on their camera phones -- -- quickly posting the images to youtube. the epicenter of the quake was in guerrero state, midway between oaxaca and acapulco, two of the most popular spring break destinations for young americans. president obama's daughter malia is in oaxaca with a group of school friends. according to the white house she is safe. oaxaca's governor says 500 homes have collapsed in his state. seismologists say the quake struck at a shallow depth, which tends to make the shaking even stronger. in the capital, miles away from the epicenter, lawmakers evacuated the chamber of deputies. panicked office workers rushed into the street, too scared to stay inside. >> "i was on the 27th floor," said one woman. "i felt a sudden drop and then everything started to tremble." >> reporter: mexico straddles one of the most active "thrust fault lines" in the western hemisphere. in the past century, there have been more than 28 quakes greater than magnitude 7. the big one -- in 1985, killed more than 100,000 people. >> what about the fault lines running under california? any additional seismic activity today? >> well, mexico's fault lines are linked to california's, so it's natural to worry. but have a look at the u.s. geological survey map. in the past hour, we've had one small quake, maybe two by now. over the past 24 hours, a dozen or so, too small, most of them for anyone to feel. over the past week, more than 300 small earthquakes. this is earthquake country, after all. the seismologist we spoke to today said this one in mexico was too far away to have an impact in california. let's hope they're right. >> david, we thank you and the abc news team in mexico. turbulence of a different kind today in the middle of the united states. a monstrous storm has planted itself on an area stretching from texas to minnesota, creating a roller coaster ride on the first day of spring. and abc meteorologist ginger zee headed out last night to watch for tornadoes. she's in temple, texas now. >> reporter: cars and flash floods, all coming from this tornado just southwest of san antonio. >> you see the metal and there are people losing it. >> this twister, one of the 312th already reported this year, almost three times the normal amount. a parting shot from one of the strangest winters in memory. this winter just didn't seem right. chicago last march, cars lost in almost two feet of snow. this year -- >> it's beautiful i love it. >> reporter: beaches blanketed in bathing suits. >> this time last year, we were still degreeing out from christmas. >> reporter: and look at this, a map of the great lakes, this year only 5% covered with ice, unprecedented in 40 years of history. in 1979, the lakes, almost completely frozen. >> this was the fourth warmest winter we've seen in over a hundred years. >> more than 1,700 record high temperatures in 36 states. in flint, smifg, air conditioning repairmen are in high demand. >> we went from nothing a week ago to everything. >> reporter: everything, as spring sweeps in on a wave of floods with a fierce storm still going strong. the thrust of this storm is enormous. it started on the west coast, from california to missouri. it has taken a long time, and it's not over. it is still barrelling east tonight. >> and the water raging behind you. thank you, ginger. there's word tonight that the fbi has decided to take action in the case of the 17-year-old gunned down by a man who said he was acting as a neighborhood watchdog. matt gutman has been investigating this story from the beginning and was struck by a nagging question about how the case has been handled. >> reporter: tonight at the department of justice investigate trayvon martin's killing as a possible hate crime, questions are piling up. did police miss a racist remark in his call to police that night? abc has also learned police haven't reached out to martin's girlfriend. why is that important? she was on the 230e7b with him as he was being followed by george zimmerman. >> the girlfriend heard everything up until this fatal gunshot and could presumably be a critical witness describing each terrified step leading to martin's death. >> he said this man was watching him. >> martin's family attorney questioned his girlfriend about what she heard that night. police have the call logs obtained exclusively by abc news and her number but according to the girl, never called. the police say they stand by their investigation. that same police department, criticized for withholding these 911 calls for sending out a narcotics officer to the scene instead of a homicide investigator. >> the police department needs to re-interview anyone and everyone. >> as for the shooter, had his father says he's not a racist. now the police department who never arrested him are under fire. . we also have news tonight have the american soldier accused of slaughtering afghan families. the lawyer met his client today and warned about leaping to conclusions. >> as far as we know, there's no eyewitnesses. as far as we know, the government hasn't been back to the scene. there's no forensic evidence. >> reporter: there are reports that he came back and said, i did it. >> that's not true either. the government paperwork they filed doesn't have that in it at all. so i'm very suspicious about that report. >> john henry brown said he's going to travel to afth to gather evidence on his own. he also took issue with that word amnesia in reference to his client, saying only his client was confused about some of the details of that night. now, to another big night in politics, your voice your vote on the president's home turf, illinois. a win there tonight will put mitt romney one step closer to wrapping up the nomination. and abc's jake tapper did the math on what that victory would cost. >> reporter: while we're waiting for official results in illinois, we'll take a look at his journey on the nomination by the numbers. >> killing time before the illinois primary returns come in, mitt romney participated in a google-plus hangout this afternoon. >> i'm going to do everything i can to bring people together to accomplish what has to be done. >> so how close is romney to winning the nomination? let's do a search of our own. not even halfway there. romney has won 521 delegates out of a total 1,144 needed to win. we still need 623 more delegates. there are still 24 states and more than 1,200 delegates left outstanding. romney has to win 47% of them. santorum has to win 67%. >> what has cost romney so far? financially romney and his allies have spent $45 million. that's $12.40 per vote. by contrast, santorum and his allies have spent $3 per vote, a relative bargain. let's look at the political cost. how negative have the romney tv ads been? 86% of the ads from romney have been negative and that too has exacted a price. so how popular is romney now? last september more americans had a favorable view of romney than an unfavorable one. it's now the opposite. more americans see him unfavorably. dia diane, preliminary exit polls indicate mitt romney may be facing a much more welcoming electorate in illinois than mississippi or alabama. he may have been better able to relate to the average voter. >> thank you, jake. and here's a photograph for the history books, queen elizabeth celebrating her diamond jubilee, marking 60 years on the thrown. among the 400 guests at westminster hall, the queen chose to single out one person for thanks, her 90-year-old husband, prince philip. >> prince philip, is well known for declining compliments of any kind. [ laughter ] >> but throughout he has been a constant strength and guide. >> they've been married 65 years and recently prince harry, her grandson, said it was him who gave him the strength to carry on. why an aspirin a day could keep cancer away. a new secret weapon in the fight against cancer. abc world news with diane sawyer, brought to you by auto stop. [ male announcer ] that. right there -- reminds you why you fell in love with her in the first place. and why you still feel the same. but your erectile dysfunction -- that could be a question of blood flow. cialis for daily use helps you be ready anytime the moment's right. you can be more confident in your ability to be ready. and the same cialis is the only daily ed tablet approved to treat ed and symptoms of bph, like needing to go frequently or urgently. tell your doctor about all your medical conditions and medications, and ask if your heart is healthy enough for sexual activity. do not take cialis if you take nitrates for chest pain, as this may cause an unsafe drop in blood pressure. do not drink alcohol in excess with cialis. side effects may include headache, upset stomach, delayed backache or muscle ache. to avoid long term injury, seek immediate medical help for an erection lasting more than four hours. if you have any sudden decrease or loss in hearing or vision, or if you have any allergic reactions such as rash, hives, swelling of the lips, tongue or throat, or difficulty breathing or swallowing, stop taking cialis and get medical help right away. ask your doctor about cialis for daily use and a 30-tablet free trial. but also a caring touch. you learn to get a feel for the trouble spots. to know its wants... its needs...its dreams. ♪call 1-800-steemer. you wouldn't want your doctor doing your job. so why are you doing hers? only your doctor can determine if your persistent heartburn is actually something more serious... like acid reflux disease. over time, stomach acid can damage the lining of your esophagus. for many, prescription nexium not only provides 24-hour heartburn relief, but can also help heal acid related erosions in the lining of your esophagus. talk to your doctor about the risk for osteoporosis-related bone fractures and low magnesium levels with long-term use of nexium. possible side effects include headache, diarrhea and abdominal pain. other serious stomach conditions may still exist. let your doctor do her job, and you do yours. ask if nexium is right for you. if you can't afford your medication, astrazeneca may be able to help. now the big headline today about health and something we all have in our medicine cabinets, an encouraging possibility that aspirin could be a weapon in the fight against cancer. abc's lisa stark on the news that could affect everyone tonight. >> reporter: it's a daily ritual for millions of us. nearly a third of middle aged americans regularly pop aspirin to prevent heart attack and strokes. but new studies suggest this simple pill may also protect against another killer. >> this is the largest body of evidence that suggests there may be an effect of aspirin on reducing cancer. >> we already knew it cut the risk of colon cancer. now many other cancers may be added to the list, including stomach, lung, prostate and ovaryian. those who took aspirin every day, appeared less likely to get cancer, to have it spread, and to die from cancer. the study suggests it takes years of aspirin use to get the benefit. if you're on a low-dose, at least five years, and even on a higher dose, three years of a pill every day. doctors warn the research is not conclusive. other studies with people who took aspirin every other day show no cancer benefit. aspirin can have toxic side effects, including internal bleeding. but today's research brings us tantalizingly closer to determining if this age-old wonder drug may be a modern miracle worker. and i want to bring you dr. karen latimer who consults with abc news on health issues. let me get this straight because this is astonishing news to a lot of people. if you're taking a low-dose aspirin, if can take about five years for the benefits to kick in, according to the study, take a full aspirin, three years to kick in, right? >> that's right. that's what the study is showing us. it's also showing that people who take aspirin every other day, there's no benefit. >> so you have to take it every single day. but doesn't that affect your stomach, stomach bleeding? >> certainly people should not be taking it, but the risks do include bleeding in the stomach and intercranial bleeding and a small percentage of people will experience these adverse risks approximate upon. >> and taking aspirin with food doesn't help. so the number one thing is go and ask your doctor. make sure you don't start this before you ask your doctor. >> absolutely. people need to talk to their fissions. there are many reasons not to take aspirin. >> this would be amazing news if something we all have in your medicine cabinets could have an effect on cancer prevention. thank you very much. coming up, it's the hot new gadget, but is the new ipad too hot to handle? reports of the ipad heating up to 116 degrees in the palm of your hand. very store in the franchise to get the word out. that could work. or you could use every door direct mail from the postal service. it'll help you and all your franchisees find the customers that matter most -- the ones in the neighborhood. you print it or we'll help you find a local partner. great. keep it moving, honey. honey? 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[ male announcer ] dosing and application sites between these products differ. women and children should avoid contact with application sites. discontinue androgel and call your doctor if you see unexpected signs of early puberty in a child, or, signs in a woman which may include changes in body hair or a large increase in acne, possibly due to accidental exposure. men with breast cancer or who have or might have prostate cancer, and women who are, or may become pregnant or are breast feeding should not use androg. serious side effects include worsening of an enlarged prostate, possible increased risk of prostate cancer, lower sperm count, swelling of ankles, feet, or body, enlarged or painful breasts, problems breathing during sleep, and blood clots in the legs. tell your doctor about your medical conditions and medications, especially insulin, corticosteroids, or medicines to decrease blood clotting. talk to your doctor today about androgel 1.62% so you can use less gel. log on now to androgeloffer.com and you could pay as little as ten dollars a month for androgel 1.62%. what are you waiting for? this is big news. when apple released its newest ipad last week, they expected it to be a hot item, but maybe not this hot. a recent test by consumer reports showed that with constant use, the new device heats up to as much as 116 degrees. that's only 13 degrees hotter than the ipad 2, and no injuries have been reported. alel says the device operates, quote within our thermal specifications. tonight an inspiring answer to a question basketball fans have been asking for two years. why does the number one women's basketball recruit suddenly quit the country's best college team? abc's josh elliot brings us a story about a young woman's choice between family and fame. >> reporter: alain dela don was the player everybody wants, the number one recruit in the country. so it was no surprise when she announced she was going to u con. a women's basketball power house. just 48 hours after arriving on campus, she left in the middle of the night. >> there's no way that this happened. how does she get home? >> it turns out, she went home in the university of delaware, just a 20-minute drive from her family's house. little did people know that what lies at the heart of her decision was the unshakeable bond between alaina and her older sister, lizzie. born deaf, blind and with cerebral palsy. >> physical contact is the only thing she knows. so i lost lizzie. >> at delaware, alaina played no basketball for a year, astounding fan, until the passion for the sport she loved was too much to ignore. but win or lose, alaina will return home once again. her purpose now clear. bearing a soft kiss for her sister. alaina is the star of her team. she led them to victory in 31 games. they lost just one. they play again tonight, and you can watch the game on espn2 or espn3 at 9:30 eastern time or 6:30 pacific. coming up, does this picture help solve the mystery of what happened to amelia earhart? tonight hillary clinton is trying to crack the cold case. i used to love hearing that phrase... but not since i learned i have... postmenopausal osteoporosis and a high risk for fracture. i want to keep acting but a broken bone could change that. so my doctor and i chose prolia® to reduce my risk of fractures. prolia® is proven to help make bones stronger. proven to help increase bone density. i take prolia®. it's different. it's two shots a year. 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