Question

Why did the intruder want to impersonate gerrard? was he successful in it?

Answer 1

Gerard was of same height and physique as of intruder, so he planned to take his identity to skip police. No, he did not succeed, as he was dodged by Gerard 

Answer 2

Here is your answer :-

Gerrard looks much like the intruder. The intruder is a murderer. The police is after him. He hopes he can easily impersonate Gerrard escape being caught.