it says colusa county sheriff's office, no street address. hand corner it says ayala case and then there's eight stamps on it. and it was pretty light. so it was way too much postage. >> reporter: because inside was just a single sheet of paper. an open letter to the cops. what did that letter say? >> basically it was claiming responsibility for the bombing. >> reporter: the letter, full of misspellings and bad grammar, had been written on a label-maker, then photocopied. its author claimed to be a military trained contract killer who'd been hired to kill roberto over a "mexico deal gone wrong." >> and that it was ms-13 behind it. >> reporter: what the heck is ms-13? >> mara salvatrucha. it's a violent el salvadorian, criminal street gang. >> reporter: and that roberto was supposed to be a target of this group? >> the letter implied that roberto had messed with a drug cartel and that ms-13 had been contracted. >> reporter: the author of the letter taunted the detectives, writing that "lab results" would find military grade powder but no dna.

. >> one thing that is unique or special about colusa county, any time i had a big case, i can go intoose get twisted fast. >> they get twisted really fast. it was constantly you know pete moore did it. my response was that's not the direction i'm going in. >> not the direction at all. in fact, they were about to put pete on the prosecution team as a key witness against paul. making pete work with the same people who at one point were hoping to put him in prison. that uncomfortable fact was irresistible for paul. pete's first day on the stand. >> it was pete said the defense, pete had the motive to kill man and implicate another. a master plan that gave him everything he wanted. >> peter is the one who indicated i have been in landscaping for 20 years. i am broken down. i want to be in the farming operation. what better way to take out roberto and paul. ye-aaah. that's cool. noooo... how much are you spending per month? $110 bucks $120 bucks $330 yeee-ah... what if sprint could cut your rate plan in half? and give you unlimited talk and text in the u.s., and match your data. goodbye ve