'GBC's torso was "covered in scratches" ........seems to indicate that he must have been at least semi-unclothed....as he told Police.....he went to bed at 10pm.
I doubt he would have been walking around shirtless. The police would have asked him for an examination, probably got him to take his shirt off for an inspection. Probably looked at his hands too. I think it's a police practise and I think if you refuse it's grounds for arrest.
I know for sure that airport security have that power. Heck, they can make you drop your pants, bend over and cough, so you can bet the police have the same authority, I'm pretty sure they do.