[He doesn't wait a second longer. Nothing was going to stop him from getting to her as quickly as possible. The most stressful part of all this is that he doesn't yet know what happened, so this could be much more worse than he could ever imagine, and that didn't sit well with him. At all.
When he gets to the apartment, he contemplates knocking loudly for a split second before remembering that that could cause a ruckus, which would be a terrible idea. This isn't the time to be drawing attention to himself.
While he is afraid of what he'll find on the other side, he lets himself in. He was a cop, is what he thought himself. He has seen it all, so he shouldn't be afraid. But he is.]