Maybe I’m just face-blind or being dense but the photos from the scene of the crime look like a different dude than the ginning hostel check in guy. The jackets and backpacks are different. Although people can have multiple jackets and backpacks. We don’t see much of the shooters face but the eyebrows look different. Although, people can pluck/shave eyebrows. I guess the happy hostel guy would have come forward and been like “WTF?” and “I have an alibi” if it wasn’t him?
Why so aggressive? They might not be confused. They could just as easily be deliberately lying to frame someone else since the real killer is gone and that makes them look bad.
Hanlon’s razor: never attribute to malice that which is adequately explained by stupidity.
That said, we’re talking cops here, who are notorious both for being malicious (ACAB) and stereotypically incompetent, often at the same time, so the usual odds (which massively favour incompetence, hence the adage) might not apply.
Also, a lot of people feel sympathy for this particular murderer (and / or enough well justified, earned, and deserved antipathy towards the victim that it overcomes what antipathy towards murderers they might normally have), so they might be aggressive towards anyone who appears to favour him getting caught.