So what I'm led to believe from the game and dialogue between Mike and Dave the FIB man, is that Mike led his crew into the North Yankton heist 10 years prior knowing that is was a set-up/ambush.
Mike tipped off/told(?) the FIB (specifically Dave) about the job they were about to do and this led to one member being killed (Brad) and Mike himself being shot whilst Trevor managed to get away and go into hiding for 10 years. Trevor assumed he was the only one who made it as Brad got locked up and Mike (and the FIB) created a false funeral for himself.
Why would he do this? He "cut a deal" with the FIB...in exchange for what exactly? What would the FIB get out of this, Dave specifically? I understand that Mike was a notorious criminal and that "killing" him catapaulted Dave's career. But that's a kind of flimsy premise...
They cut a deal with him and set him up with a luxury mansion in the hills...wtf are the FIB getting in return? Why wasn't he just jailed? Why would the FIB go to through all the trouble of setting him up in a witness protection program (this was mentioned by Lester at one point in the game)? Would he have testified against Trevor (or someone else) in court or something? Did Mike want out of the game because of his family and wanted a new start, so to speak, and the only way to get this was colluding with the FIB in order to catch his associates (i.e Trevor, Brad)?
This is a terrific game, I enjoyed playing it but thinking things over, this just doesn't make any sense to me.