Tina says this in the HBO documentary.
I've been a proponent of the bomb being real for some time now. I think that he would have only used it if he got cornered. Bomb serves two purposes if you set it off: it kills you but it also likely makes your remains unidentifiable. If he was killed in a shootout or something and they couldn't figure out who he was, you can bet for damn sure they'd have thrown his dead face into the papers asking "do you recognize this man?". So blowing yourself up eliminates yourself but also eliminates you being ID'd if you were peraps worried about bringing embarrassment and shame onto your family.
While at CooperCon, I showed Kaye the statement that Tina made from the cockpit describing the bomb. He had never seen it before. One of the guys at the table had a brother who worked in Hollywood as a pyrotechnics guy and he called him to figure out how many amps (or maybe volts) it would take to set off a blasting cap for dynamite. Whatever that battery was (Tom knew what it was from Tina's description) certainly had enough juice to pop a blasting cap. So there's nothing to rule it out being real.