Or is it possible that the slip of the tongue by the parent was actually planned by the investigation team? Might it be a trap to catch the killer?
No. That is never a good idea. Releasing information can only hamper the investigation. Especially when giving out information that only the suspect(s) would know. Like the point of entry, they location of the victims, they type of knife, etc. They just lets the suspect(s) know what’s up.