My interpretation of the novel is that this is exactly what happened. The owner of the flat made the decision to cover up the murder in order to avoid losing money. Everybody in Bateman’s world is utterly self-absorbed and completely amoral; and they’re all so obsessed with surface and status that they’re almost a set of attitudes rather than actual physical creatures, which is why the lawyer thinks he had dinner with Paul Allen. He didn’t, it’s just that he didn’t realise. At the dinner he probably didn’t interact with his guest, beyond the handshake and exchange of business cards. American Psycho takes place in a world where no-one connects with anybody else.
The general theme is that Bateman gets away with utterly savage crimes because no-one suspects him - on the outside, he’s anonymous - no-one cares for the victims, he has no shortage of resources, everybody is out for number one, and no-one really benefits from investigating his murders. The world is all surface and there isn’t an ounce of human compassion or feeling.
From what I remember he does get caught at one point, by a taxi driver who realises that he is the mass-murderer who has been going around killing people; but Bateman bribes the taxi driver, who lets him go, because he is just as insubstantial as everybody else in the book. The novel gives us one little bit of hope that this monster might get his comeuppance, and then destroys it. Who is going to stop him? The police don’t really care. He’s never going to feel any remorse. He’s untouchable. On a metaphorical level he’s one of the vampire parasites that rule our lives.
“Outside the limit of our sight, feeding off us, perched on top of us, from birth to death, are our owners! Our owners! They have us. They control us! They are our masters! Wake up! They’re all about you! All around you!”
Now, it’s not necessarily realistic - it seems odd that he would get away with killing the kid - but there’s a big difference a work of fiction that takes place in an exaggerated world, and an out-and-out dream sequence. The film is a lot more ambiguous, but again there’s a theme that Bateman exists in a refined world where human compassion doesn’t exist and people mean nothing to each other.