When it came down to the three of them...
What was Lucas expecting to happen? I mean, if Sara did end up having to shoot Gabe- it would then be obvious that she wasn't the killer and Lucas would get caught (even if he killed Sara too.)
shareBefore getting shot, he said "There's no evidence against me. If you shoot me now people will think you did it". I think he expected to kill everyone and then kill himself so that no one would know who the killer was. Remember: He wanted to prove he could do it.
shareOh okay, I gotcha. Thanks!
shareWhy kill himself? He'd framed Sara for the whole thing, could have
killed her and claimed self-defence.
Note that he kept on having to defend Sara to the others, he was
setting up the frame but for later... but didn't want it to convince
the others too much while it was all going on.
It took me a while to get too. He was trying to pull off another CROATOAN legend- hence the reference. I forgot that he probably wasn't counting on Gabe, who put a big dent in his plan.
He wasn't actually framing Sara for the whole thing. He just needed to throw suspicion around in the group and the only way to pass it to Sara was to frame her. Then he just told her that he was setting her up so she would hesitate and he could drown her in the water (which would have fulfilled his original plan. Remember that he thought Gabe was already dead.) He would have cleaned up the evidence incriminating Sara so the whole thing would be ambiguous.
The way he saw it, a case of a mass murder of the best FBI agents going cold would be legendary. I believe he even said so himself- to Sara towards the end.
--> Put simply:
His original plan: kill each FBI agent with their weakness leaving Sara as the last one (because she'd be the easiest to finish off- he'd just have to lead her to the water. He figured she wouldn't kill him them because a) she'd be too freaked out in the water b) he'd threaten to frame her for the whole thing and she'd hesitate.)
The dent: Another person showed up. A really smart person who's weakness Luke did not know.
Luke's big mistake: Waiting to kill Gabe. He wanted to keep him around so he could figure out his weakness and use it against him to kill him. But he never figured it out. And it took too long because everyone else died first. So when it should have been just Luke and Sara left (his original plan) Gabe was still alive too.