Came up with this theory... This picture here could have been taken from the final mission of the game. My guess on what's happening.
Franklin picks up Trevor from his house. They are preparing for the final bank heist.
Franklin: "Where's Michael. I thought he was with you?"
Trevor: "He didn't call you? He wants us to pick up some gear from a buddy of his in Jefferson Park and then meet him in Vinewood Hills."
Trevor: "Assault rifles, vests, ammo, everything we need to pull this sh*t off."
Franklin: "I thought he was taking care of that?"
Trevor: "Somethin' came up I guess. He called me and gave the orders. I don't know what he's doing."
Franklin: "Don't you think Michael is acting a bit strange? Why the sudden change of plan?"
Trevor: "What are you worried about? He probably went to find us a new disguise or something. Mikey always does that."
Franklin: "Probably. Seems suspicious to me, though..."
Franklin pulls out of the drive-way. In the back alley across the streets from Trevor's house, an all black is parked. Watching. Once they start down the street, the copter begins to follow them. Franklin and Trevor don't notice it until they are on the high-way, half way to their destination.
Trevor: "Why the f*ck is that sh*t following us?" *points at the car*
Franklin: "Wanna take them out?"
Trevor: "You're damn right I wanna take 'em out!"
Franklin exits the high-way and begins to speed up. The car easily matches the speed but continues to keep a safe distance. Franklin leads them to the local junkyard in central Los Santos. They exit the car and see the headlights of the black vehicle approaching. Trevor pull out his pistol and Franklin grabs his shotgun from the trunk. The two walk into the junkyard and cover behind two separate dumpsters. Three men dressed in suits exit the vehicle. One of them pulls out a flashlight. Another uses the police dispatch. Cops.
Gregory: "Los Santos F.I.B agent Gregory Nelson requesting immediate back-up to Courtney's Junkyard."
Unidentified Cop: "They notice our tail. Go loud!"
The cops rush the junkyard and begin to open fire. at various hiding spots. Trevor removes himself from cover and shoots one of the officers in the chest twice. Before the cops can open fire on Trevor, Franklin comes out of cover and begins to fire shotgun rounds at them. The sounds of sirens in the distance blared through out the streets. Their back-up was on the way.
Franklin took down an officer.
Franklin: "We've got to make a run for it!"
Trevor: "We're surrounded you dumbass!"
Franklin: "No we ain't!" *points and a torn down fence in the back of the junkyard*
Trevor makes a run for it, shooting behind him as more police entered the junkyard. Two cops run after Trevor. As they run by, they do not notice Franklin, giving him an opportunity to land a clear head shot on an officer. Franklin could see men dressed in bullet-proof clothing and ski-masks now. They S.W.A.T had arrived. The lasers from their assault rifles scanned the area. Franklin began to creep away. He considered himself lucky that it was getting dark. They would have spotted him by now.
Trevor was running as fast as he could from the police officer. The cop pulled out a walkie-talkie just as Trevor made it into a near by alley. The cop hesitated to walk in, but he figured that Trevor must have been afraid since he was running away.
Cop: "Suspect is about 6 feet tall with grey colored clothing under his jeans-jacket. I think I've got him trapped in the alley next to Grimswood Bar."
Trevor was prone. The cop walked right pass him. Before he could turn around, Trevor grabbed him from behind and slit his throat wide open with a piece of broken glass. He then took the dead cops gun, just to have a back-up weapon. Trevor walked into the street and a red top-less sports car was driving by. Trevor pulled out his pistol and ran over to the car, killed the passenger first, and aimed at the woman driving.
Trevor: "Out of the car!! Out of the f*cking car right now, bitch!!"
Woman: "Okay, okay!!!! Whatever you do, don't shoot me, please!!"
Trevor got into the car and tossed the dead body out. He then made a U-turn to head back near the junkyard, only to see if Franklin was still alive.
Franklin couldn't escaped. As long as he remained hidden then he had a slim chance of surviving but the S.W.A.T had covered the only exits. Shooting his way out was impossible with a shotgun that was low an ammunition already. All of a sudden, Franklin's phone vibrated. It was an unknown number. Detective Gregory Nelson was holding up his phone.
Gregory: "You didn't escape, Franklin. You're in here and I know it. Come out so we can talk about this."
A helicopter with a search light was coming. Franklin's heart was pounding. The police were going to kill him for sure.
Gregory: "There! I see him over there!!"
The police ran right by Franklin's hiding spot and aimed their guns at a near by hobo.
Hobo: "What the hell ya'll motherf*ckas want from me?!"
Franklin dropped his shotgun and ran through the open gate. The police noticed and fired several shots at him but in moments he was out of range. Just as he ran into the street he had almost been run over by a red sports car. Trevor was driving.
Franklin:"Watch where the f*ck you drivin'!"
Trevor: "Hurry the f*ck up."
Franklin jumped in the blood stain passenger seat and they drove off. Once they got back onto the high way Trevor decided to call Michael. The phone rang three times before he answered.
Trevor: "It's all f*cked up, man. We nearly got our asses pinched."
Michael: "What happened?"
Trevor: "Police followed us. we tried to take them out but it got too heavy. We managed to get the hell out of there."
Michael: "We'll talk about this when we meet up. Same spot as we planned."
Trevor: "Got it."
Trevor hung up the phone.
Franklin: "What did he say?"
Trevor: "We're still meeting up. I guess we're going to re-plan this sh*t."
Franklin: "I think he set us up, man."
Trevor: "Mikey? Why the f*ck would he set us up?"
Franklin: " I don't know. He's always acting strange whenever he gets a phone call, as if he's got somethin' to hide. And his sudden change of plan was just too suspicious. We had it planned out for weeks and he flipped the whole plan around. Don't tell me you think this sh*t is all coincidental."
Trevor: "I've known Mikey all my life. You keep talkin' about him like that and I'll put a f*cking bullet in your skull, you got that?"
Franklin laughed. He never like Trevor. Every time they met up there was always a violent tension, as if the two of them could begin to fight each other at any moment. Franklin planned on killing Trevor soon, but he didn't want to destroy his partnership with Michael.
Franklin and Trevor have arrived to Michael's location.
Michael stood and waited for them to exit the car. Trevor got out and walked up to Michael.
Trevor: "f*ck are we gonna do? This was the BIGGEST heist we had planned and it all got f*cked up."
Michael: "If the cops were tailing you then it's obvious they didn't know where you were going. They must be after me, too, then."
Trevor: "How the f*ck did the cops get so much info on us? We've done everything without a trace."
Michael: "I don't know." *phone rings*
Franklin got out of the car but did not approach them. Instead, he leaned against the car. Trevor stepped back and joined Franklin. Franklin watched Michael as he answered the phone, studying his every move. Trevor looked out into the distance.
Gregory: "Michael, we didn't get 'em. I traced the location of Franklin's cell phone and according to the radar he's with you right now. Is that so?"
Gregory: "S.W.A.T on the way, we're going to take 'em in or out. You'd best try to clear the area."
Michael: "Will do."
Michael hung up the phone and looked at Franklin.
Franklin: "Who was that?"
Michael: "James. He wants me to pick up some stuff for him on my way back."
Franklin: "Oh." *looks away*
Trevor: "What are we going to do about these damn cops, Mikey?"
Michael: "...f*ck the cops. If tailing you guys is the best they can do then don't really know what we're up to. They want to catch the three of us together I suppose. Probably to interrogate us about the recent heists. That means that there is a rat among us. Someone that knows something about us, but not enough to give the cops something to go on. We're cutting all links between us and the heists immediately."
Trevor: "What do you mean?"
Michael: "Anyone the three of us have affiliated ourselves with is going to die."
Trevor: "That's why you're the boss. I'm out of here. I'll go whack Pete tomorrow. Never liked the guy."
Franklin: "Hold on, Trevor."
Trevor: "What is it?"
Franklin walks up to Michael.
Franklin: "Let me see your phone."
Michael: "For what?"
Franklin: "You got somethin' to hide?"
Trevor: "Calm the f*ck down, Franklin. You're making an ass of yourself."
Franklin: "If you've got nothing to hide, let me see your damn phone, Michael."
Michael: "No. I don't really know what your problem is. Trevor, take him home or something."
Franklin: "You said James just called you. I want proof." *reaches for Michael's phone*
Michael: "Get the f*ck off of me!" *punches Franklin*
The two began to fight. Franklin was younger and stronger so he easily out maneuvered him. Franklin tossed Michael on the ground and punched him. Michael's phone slid in front of Trevor.
Franklin: "Grab that sh*t, Trevor."
The phone rang. Trevor picked it up and looked to see who was calling. Gregory.
Trevor: "Who the f*ck is Gregory?"
Franklin: "Gregory Nelson, the f*cking F.I.B-"
Michael stabbed Franklin in the leg with his switchblade. Franklin fell to the ground ad Michael got on top of him holding the blade to Franklin's throat.
Michael: "You ignorant little sh*t. I should kill you!"
Franklin: "Answer that phone call, Trevor!"The player decides to answer the phone or to leave it alone. Whether you answer the phone or not affects the ending.
Trevor answers the phone call.
Gregory: "You cleared the area, right? I'm heading your way with the S.W.A.T. We're going to bust those two."
Trevor: "You fags ain't busting me!!"
Trevor throws the phone over the cliff. Michael started to run away, trying to reach his car. Trevor shoots at Michael and misses and he heads down the hill. Franklin gets up and the both of the chase Michael.
Trevor shot again and hit Michael in his back. He fell down and began to roll down the hill. He suddenly pulled out an Uzi and shot a barrage of bullets, all of them hitting Trevor. Franklin runs over to Michael and attempts to grab the Uzi, but Michael tosses it over the cliff. F.I.B trucks are racing to the hills. Trevor lays dead next to them.
Franklin: "What the f*ck did you do this for, man!?"
Michael: "I had to. They threatened to take my family if I didn't cooperate. I did what they wanted."
Franklin: "You piece of sh*t!" *punches Michael*
Michael: "You wouldn't understand... You're just a street bum. I'm a family man." *throws Franklin off of him*
Michael tries to escape again. Franklin attempts to run after him but the wound in his leg prevents him from getting up.
Trevor: "Franklin... *cough* ...take this pistol...waste that *cough* son of a bitch..."
Trevor slides his stolen police colt to Franklin. Franklin shoots Michael in his spine so he cannot run away. Franklin then crawls over to Michael and puts the gun to his head.
Michael: "Shoot. Shoot me you f*cking pussy! It's not like you're going to get out of this alive either."
Franklin: "Poor choice of last words, bitch."
Franklin pulls the trigger, blasting Michael's brain all over the ground. Police helicopter, F.I.B trucks, and S.W.A.T tanks all came to Vinewood Hills.
Gregory came with his pistol.
Gregory: "Freeze! You can't fight your way out of this one!"
Franklin: "Fight... I can't fight change, I can't fight gravity... I can't fight nothin'. My whole life, all I ever did was fight.'
Gregory: "What... What the the f*ck are you talking about?"
Franklin: *looks at Trevor and Michael* "Our time has passed."
Franklin jumps off of the Vinewood Hill and dies.