Remember That Press Conference on Wednesday When They Wanted To Announce an Arrest?

[Mad Scientist]

You recall that? They wanted to show a picture of a possible suspect but right as they were about to do it they get a Bomb Threat and have to evacuate the building instead.

Boston Courthouse Evacuated ? Bomb Threat: ?Code Red? Announced - Hollywood Life

Ok, so later on when the Bomb Threat was cleared the Press Conference was cancelled and there was no suspect picture shown. What's more, is the "authorities" then denied that they even have a suspect!
Uh, wat?
After 'Misinformation Flying Around,' New Video May Be Break in Boston Case - Alexander Abad-Santos and Matt Sullivan - The Atlantic Wire

CNN, ABC Boston, The Boston Globe and the AP at various points within a one-hour period mid-Wednesday afternoon reported that a person connected to the Boston bombing was taken into custody — CNN and Fox News had, minutes earlier, reported that there had been an arrest — though law enforcement went on to insist that no arrest has been made. There was significant police presence reported (by significant reporter presence) at the federal courthouse ahead of a scheduled 5 p.m. briefing by law enforcement officials after multiple outlets, based on law enforcement sourcing and also piggybacking on CNN sourcing, jumped on a "breakthrough" in the case — authorities have apparently made a big break after new video from a Lord & Taylor department store in Copley Square (just out of frame in the Reuters photo below) seems to have helped possibly identify someone connected to the bombing.

"Identify" not "Arrest". When contacted, numerous Alphabet Federal Agencies say they "haven't made an arrest".

So why didn't they just go ahead after the Bomb Scare and give out the Information about the Suspect Bomber? What changed and why couldn't they just tell us?