Johnny hadn't expected the police to enter the house directly, as he had already fired his gun. According to police enforcement practices, without having eliminated the danger, they should have negotiated with him from outside, asking him to come out, rather than forcefully entering the house.
His father was a policeman and often told him stories about police enforcement, so he was certain of his facts.
Johnny glanced at the room, realizing that jumping out of the window was not a good option. With so many police cars outside, the police must have already surrounded the entire house.
"Don't shoot, I'm coming out."
Johnny pulled open the bedroom door from one side, only opening a crack. He peeked through the gap and saw just one officer, then promptly pulled out his pistol and fired at the door.