The Bronx psycho suspected of beating a man to death because the victim held a subway exit door open for him was out on the streets despite allegedly carrying out an eerily similar attack on a security guard – who counts himself lucky to be alive.
The security guard, who asked to be unnamed, exclusively told The Post Wednesday he could tell the suspected killer — identified by sources as David Mazariegos, 25 — was a “very dangerous person” during their June run-in outside a Chelsea theater.
He said the unhinged stranger sucker punched his glasses off his face after he tried to shoo the maniac from an event for troubled kids.
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“I told the prosecutor, I said, this guy is gonna do this again, you better take him off the street before he does this to someone else,” the guard said…