Exactly, Jos. (Did you read what I wrote, Joe?). The 'unknown' (or at least, unconvicted) perpetrator is the - wait for it - 'perpetrator' (or 'offender' or 'criminal'). The 'suspect' is the person suspected of having been the perp. As I say, if you are saying that the suspect committed the crime, you are saying that the suspect committed the crime - so it defeats the purpose of calling them the 'suspect', which would be presumably to allow for the presumption of innocence.

If the 'suspect' is unconvicted, then it isn't reasonable to describe them as the 'perpetrator', as that has yet to be confirmed.