Dustin Johnson appeared in court Thursday and pleaded guilty to five counts each of attempted homicide and aggravated assault, as well as one count of arson and risking a catastrophe in the Nov. 11, 2016 rampage.
The 40-year-old had once been a resident at the Turtle Creek Valley Mental Health/Mental Retardation in Homestead, just southeast of Pittsburgh.
Witnesses told police he was armed with two knives and an air gun that looked like a real firearm. He attacked staff and residents before police shot him several times.
One person was injured critically, but all survived.
His sentencing is set for January.
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