Beyond its technical brilliance, the keys to M's lasting impact are its psychologically convincing portrait of Hans Beckert's twisted compulsion and the still relevant ambivalence of his capture and "trial." Unlike contemporary cinematic examples of the serial killer, Beckert is not presented simply as a grotesque psychopath. Nor is the issue of how society should deal with him at all clear-cut. To be sure, the gut-reaction of most film audiences is to root on the underworld mobsters and petty thieves who, beating the established authorities to their mutual quarry, capture Beckert and bring him to a mock- formal trial whose conclusion is foregone. Like many in America today, Beckert's accusers are disinclined to listen to insanity pleas and would just as soon be rid of the "monster" in the surest way possible: a summary death penalty with as little fretting about legal rights as possible. Considering the heinousness of Beckert's crimes and the imperfections of a legal/medical system that could well turn him loose to kill again, this emotional response is hard to resist. Yet M is by no means an endorsement of vigilantism - quite the contrary. Through the unlikely rhetorical persuasions of Beckert's unkempt "court appointed" defense attorney and Beckert's own impassioned monologue, Lang strongly implies that impatience with democratic judicial procedure and a paranoid eagerness to scapegoat others (guilty or not) in the name of order are symptomatic of the social hysteria breeding Nazism in 1930s Germany. That the ruthless killer who heads the underworld looks, dresses, and gestures like a Gestapo officer is no accident. Moreover, the letter "M" chalked on Beckert's back by one of his pursuers not only stands for "murderer" but also alludes to God's marking of Cain. While the popular misconception holds that the mark of Cain symbolizes his evil, it in fact represents God's warning to Cain's flawed fellow creatures not to mete out wrathful vengeance, but to leave justice in God's hands. Translated into secular terms (and literally entering the shot from the top of the frame), God's hands in M belong to the legitimate authorities that intervene at the last moment to arrest and try Hans Beckert "in the name of the Law."

when reporting that he wasn't involved, refers to him as a "witness"

Possibly due to the fact that by the time he was listed as not a person of interest, we learned that he was going to be deported for national security reasons. Which doesn't necessarily make him not a victim, but it does sort of muddy the waters. And reporters often struggle in those situations.

Monday was Patriot's Day in Boston.

Which, as yet, has no connection at all to any motive beyond the sort of rampant speculation that you decry above.

It's pretty obvious by now this was not the work of a foreign terror faction.

That may turn out to be true, but why is it pretty obvious now? All we know is that 2 explosives were detonated and the police have 2 suspects they've identified from videos and photos of the event. Their affiliation and motive is not known.

Was it a lone sicko or a domestic extremist group? That remains to be seen.

It will be one or the other.

The Aryan Brotherhood in north Texas has done plenty to instill fear in their area. (One of my sisters lives there.) People who use or threaten violence to control others shouldn't be surprised if they fall under suspicion when violence occurs.

It's pretty obvious by now this was not the work of a foreign terror faction.

While I agree, it's still speculation.

It's human nature, it's what drives innovation and advancement, and there is nothing wrong with it so long it based on something beyond fear.  It's how the human brain solves problems.  

The real problem to me is 'news' organizations, who people look to for facts, have long ago realized that there's money in speculation, even when they are wrong.  News should be the source to take all the speculation and and investigate and reveal what happened, not what some clown thinks probably happened.