The ending wasn't clear...SPOILERS
I really liked the movie. I'm hoping that the BBC mini-series is more clear at the end, but if it's not I won't be too disappointed....
The end could be interpreted several ways...I don't want to spend too much time going into detail but here are a few notes..
When Bingham goes to the government building...He couldn't have been after Cal specifically. He doesn't even know that he is there. Anyway what would be the purpose of killing Cal. Others had the story as well...But maybe Bingham didn't know that yet. Maybe all he knew for sure is that Cal had seen him and was onto him. But Cal had already gone to the police...
It seems to me that Bingham took it upon himself in his insane state to decide to go to the govt building and wait for the govt officials that are in Point Corp (especially Fergus) and gun them down when they got to work in the morning. He was probably on a suicide mission as well and if he hadn't been shot (by the police that happened to be there) he would have decidedly committed suicide after he shot as many people as he could. Clearing any possibility of him becoming imprisoned and forced to talk. He had dressed in his military garb after all, and usually that signifies getting dressed up for a suicide mission in a case like this. Other times we had seen him he was dressed as a civilian.
As far as Bingham's phone call at the end...
(1) We don't even know for sure that it was Stephen!
(2) Whoever he had called had no time to respond at all. His message was short and fast. Then he hung up.
(3) Maybe he left a message, although that seems weird that he would do that (security reasons), but he was insane.
Other interpretations I have read on this board do not make any sense to me. I'm looking forward to watching the BBC series.
But who knows, maybe Stephen was a psychopath who was super jealous of Cal sleeping with his wife (kill him, especially since he knows everything!), wanted his girlfriend dead (she's Point Corp! Kill her!), had no real emotions and could easily fake tears..... If I was his wife I would watch my back....NOT!