Totally agree with the above. They know who it is. Think about the risk / reward ratio of releasing this information if they don't already know everything they need to know: how many people, realistically, are going to remember chatting to this profile four / five years ago? LE would already have followed up on every IG account he's following in private. Anyone else remembering anything is unlikely, so the "reward" chances are low. Conversely, there's the "risk" that the killer deletes his accounts and destroys evidence. If they don't know who it is, that risk isn't worth it.
LE will know this. They're provoking a reaction.
A possible reason for the night time announcement: get the killer to see it when they wake up, and they react when they're least likely to think clearly. At the same time, if he saw it at night before going to bed, any suspicious activity at that time of night stands out as even more suspicious to a partner / spouse.
