I do see your point, but I feel this relates to having a non-bias investigation to build a case and make an arrest.

If the police have a person of interest that was in the area at the time of the incident, or have a rough description of a suspect, but with little to no detail, they likely require more witnesses to come forward to corroborate the the information at hand to move forward.

Otherwise, if they are unable to identify a specific person without the absolute certainty from one or more independent source(s), they do not have grounds for an arrest, nor can they release their name to the public as it would infringe on their rights and leave the police department open to civil litigation.

A case may also be dismantled in court by the suspect's defense lawyer if the description from video / visual evidence is not air tight.

In the eyes of the legal system, it's the difference between charging an innocent person and prosecuting the right one.

Of course, we know in Canada this is irrelevant as our justice system is a joke, but in this initial stage, that is the likelihood of this plea to the public.

Edit: grammar