It's clearly established that Jackie Leroy lives on the top floor of her shared house, in Flat 8. Fenton, however, doesn't press an entry buzzer at either end of the eight-buttoned door panel (so actually buzzes Flat 4 or 5) yet stills gains entry to Jackie's flat.
When Fenton is questioned by the police, he says he never saw a cigarette lighter by the body, but earlier, when Fenton discovered the body and examined it, the cigarette lighter can be seen lying by the body just above the knee.