I'm not sure how you prove that someone lied "on purpose", rather than just were mistaken, "celebrating", inaccurate, took information they wanted to be true and clung to it, etc. I've said repeatedly that LE were heroes that day so clearly not bashing their profession, but certainly
if someone including LE reports misinformation during a sensitive time there shouldn't be a conspiracy of silence, as if saying that they reported something incorrectly (with whatever motivation they had in the moment, good or bad) was "bashing LE" as a group. This same group of LE happens to be "my" LE, as I'm from Boston, and I do want to know that they will communicate with me as best they can while on the job, and am grateful for their service last week that kept my family safe as well.
However, yes they said things that were later shown to be untrue - call it what you will, a mistake, a mistruth, a miscommunication, whatever feels most appropriate.
http://www.salon.com/2013/04/25/the_changing_facts_in_the_boston_investigation/