How did he know…(SPOILER)

…the woman he loves killed his father? He tells the guy at the bar who of course is the same one she confessed to in the Metro, but I did not see anything showing how he found out. Was it something to do with her car and his part in the investigation? For that matter, how did they even know to send a diver down there? This film was quite short and it seems to me it could have been a bit longer.