A son locked in a closet by his mother in a thriller movie

I’m looking for a movie, either American or British, probably from 1995-2013, I think it was a thriller, it was watched between 2009 and 2015. A boy is locked in a closet by his mother because she brings her lovers home. The boy watches everything through a crack in the closet. They are not wealthy and live in some industrial district. The film ends here. Years pass and the boy is shown as an adult man, maybe 50-60 years old, walking through the industrial district to his home with a briefcase in his hand. He wears glasses, is slim, and wears a coat. He enters a house with an old bed, possibly his family home. I know that he kills prostitutes, has a childhood trauma, brings women home and kills them there. It is neither Citizen X nor Maniac (1980).

I have not seen this, this is just a guess, and it is titled “Maniac”, but it is not the 1980 movie, and the timeframe is a match. Maybe?:

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