I think if they were at the stage of 'knowing' who it was, they definitely wouldn't have announced anything that would warn that person.
For example, when they were staking out Bruce McArthur's apartment, they knew it was him, but were watching for more evidence (IMO where he'd hidden the bodies). As soon as someone else was in danger they swooped in with the arrest warrant already in hand,
IMO they don't know who the perp is, they just have someone they'd like to interview or get info from, which could result in clearing them completely. "The goal of any investigation is to identify persons who may have been involved in an offence or to exclude them as suspects."
So the person of interest 'may have been involved or may still be excluded as a suspect'. As I mentioned, IMO that person is not cooperating in the investigation and that's why this info is being released publicly, to send a message to that person. (I believe I have seen this before, but of course, LE don't share their intentions about these releases).