want to give you a little background on ossterman. he s his best friend. here s a little bit more about him. this is from david mattingly. reporter: when george zimmerman was worried about an aggressive neighborhood dog, he bought a gun and went to his friend, david ossterman. once you get married, he changed his perspective in life and that he was not responsible just for himself but his wife. ossterman helped zimmerman weigh the prois and cons on how to choose the gun. it was easy to conceal and carry. acting on osterman s advice, zimmerman carried it everywhere. always. he carried it always. the one thing i did tell him the
reason for doing that, if it was on your person, it can t be anywhere else. reporter: it was on his person the night he encountered trayvon martin. he told osterman how he grabbed it during the fight. according to what he told me, when the head bashing on the concrete stopped and trayvon reached for the firearm that was at his side, grabbed ahold of it. reporter: osterman quoted it in a book. somehow i broke his handle on the gun. i got the gun in my hand, raised it towards the guy s chest and pulled the trigger. and this is where the problem lies for george zimmerman because comments quoted by his friend ossterman do not match what zimmerman told police. listen to what he says as he walks investigators through the crime scene. and he reached for it. i felt his arm going down to my
testimony couldn t help zimmerman. i only heard the story twice, and whether it was grabbed the gun, grabbed for the gun, i just perhaps it was just the intent. but i believed he said he grabbed the gun. reporter: months before the trial, osterman, a federal air marshal, described to me in detail how he helped zimmerman weigh the pros and cons before he settled on buying a thin, lightweight .9 millimeters. it was easy to conceal, easy to carry. and acting on osterman s advice, zimmerman carried it everywhere. always. he carried it always. the one thing i did tell him, for the reason for doing that, was if it is on your person, it can t be anywhere else. reporter: it was on zimmerman s person the night he shot and killed trayvon martin. and osterman told me it s hard to answer the question does he feel any regret for the advice he gave? so i would wish it had never
tunnel vision. he was able to smack the hand away from the firearm, and that s when he drew the firearm and fired. reporter: osterman wrote about it in a book, quoting zimmerman somehow, i broke his grip on the gun where the guy grabbed it between the rear site and the hammer. i got the gun in my hand, raised it toward the guy s chest and pulled the trigger. and this is where the problem lies for george zimmerman, because comments quoted by his friend, osterman, do not match what zimmerman told police. listen to what he says as he walks investigators through the crime scene. and he reached for it, but he reached like, i felt his arm going down to my side, and i grabbed it and i just grabbed my firearm and i shot him one time. reporter: in multiple recorded interviews, zimmerman never tells police that trayvon martin ever touched his gun. and i saw him take one hand off my mouth and slide it down my chest, and i just pinched his
arm and i grabbed my gun and i aimed it at him and fired one shot. reporter: dna testing seems to agree. there was no trace of trayvon martin s dna on the gun s grip. prosecutors list osterman s book with zimmerman s conflicting account as potential evidence, possibly to challenge zimmerman s credibility. as for his connection to the gun zimmerman was carrying, osterman says it s hard to answer the question does he feel regret. so, i would wish it would have never happened. however, the reason why george had it, it was not for malice. he didn t have it to go out and commit a crime of hunting someone down and harming them. it was for self protection. and i m glad that that firearm was used to protect george. and now david, so, if he really is george zimmerman s best friend, how does mark feel about, at this point, you re