strange incident as he was leaving one day. and all of a sudden the tire went flat. reporter: this is what flattened the tire. a homemade spike. the spike was constructed of a harvester sickle welded to a two-inch washer. further inspection of the area we found another one of these spikes. almost like a challenge to us. here i am. i m doing this to you. now come find me. basically they re coming after the cops. coming up, investigators may be able to fight back with new ammunition as they finally turn up scientific evidence on one of the letters the killers sent. there was a dna profile on the back of one of the stamps that was affixed to the envelope. when dateline continues.
reporter: so you at least had some time. maybe. maybe. dave tells me that they had received a letter and the letter had mentioned me. reporter: roberto s brother eduardo. he says be careful. watch yourself. reporter: but it wasn t just eduardo in the crosshairs. the letter writer claimed whoever was now driving roberto s now repaired pickup truck, that white f-250 the bomber wrote, is in great danger. and who was that person? roberto ayala s son, jesus. the threat against the ayalas was looking very real. it was real. it didn t just look real. it was real. a lot of sleepless nights. reporter: because this ex-marine not only had a farm to run but as he saw it a murder to solve, and now two families to protect. going through my mind was
it just beggars the imagination to think that peter would know enough about when the police are going to arrive and know that some junior officer is going to happen to notice this very faint little image of a diagram on a white piece of paper which he never would have seen if the light hadn t been just right on that table that afternoon. if i m peter moore and i engage in this and they don t find it, all right. my plan didn t work. but if they do find it, it s a home run for me. and there s very little risk to me, peter, to engage in it. it s not like i have to break into the police department and tamper with some evidence. reporter: but paul s fingerprints were all over that piece of paper. peter s were not. i would agree that that shows that this had been in the house and that he may have touched it and in fact leaned on it in the way the prints were situated
but more than one way to find a guy brazen enough to sent that material to the cops. we had the letters we wanted to get analyzed. we wanted fingerprints. we wanted dna. reporter: the letters and envelopes came back clean just as the bomber said they would. what was going on? to investigators one theory seemed the least likely, that roberto was mixed up with a drug gang ms-13. the ayalas are a classic bootstrap story. roberto, a very religious man who worked his way up from field hand to farm manager, oversaw the day-to-day operations of a multimillion dollar spread. he knew the land. he knew the machines that worked it. he was utterly committed to that work. what did working that farm mean to your dad? that was everything. it was our whole, even our lives and his life, our whole life revolved around it. we were always there and growing up. reporter: first jobs as kids, right? yeah. learned how to drive on the
something to do with roberto s murder. which placed eduardo in the hitchcockian situation of working side by side with the man who may have murdered his brother. i d look at him just like i m looking at you, talked to him just like i m talking to you, and in the back of my mind i m thinking, you re the one that did it. reporter: while that dna result from the stamp wasn t strong enough to hold up in court, it was significant enough to get a warrant to search paul s home. for whatever that was worth, five long months after the bombing. he had done some kind of major cleaning of his house. so we d actually had conversation about this and reporter: like a what s the point conversation? that was one of the things that was talked about. and the decision was made. i didn t want to leave it untouched. reporter: sure. but your expectations were not that high. no, they weren t. reporter: with just this one crack at paul s house, detective salm wanted to make sure they