Honestly, I'm surprised he didn't kill her too. But the property management company mentioned that the building had "extensive security" and if he really was a pro, he'd undoubtedly thought of various scenarios and downsides, and how he should react, long before she ever stumbled into the scene.
Could just be that he felt risking capture (after she called cops) was more important than removing the body, since it was already seen anyways.
Honestly, I'm surprised he didn't kill her too. But the property management company mentioned that the building had "extensive security" and if he really was a pro, he'd undoubtedly thought of various scenarios and downsides, and how he should react, long before she ever stumbled into the scene.