The man is a township resident, but Action News is not using his name because he has not been charged with a crime.
In a news conference, the township's police chief said the rifle-carrying man was taken into custody on Thursday on an involuntary mental health warrant.
That step was taken after friends of that man messaged police via Facebook with concerns about his behavior and change in mental status.
"These concerns would lead a reasonable person to believe that he may pose a threat to himself or to our community," said Chief Patrick Molloy.
In court paperwork one of the friends, identified as witness #2, says the young man recently texted a picture of an AR-15, stating 'look what I just got.'
He told detectives the young man always had a "dark sense of humor" and "always joked around with him about committing suicide."
Witness #2 claimed in June 2017 the young man, who was then a student at Abington High School, talked of shooting up the school, but then immediately laughed.
Witness #2 also said that, last January, the young man talked of shooting up Penn State Abington. The friend told detectives, "I think he... is throwing up some red flags because he recently dropped out of school. He gave me the impression he feels he has nothing to lose, in a way."
Detectives said in court records that they searched the man's smartphone and found internet searches including 'Parkland shooter,' 'law enforcement visits,' 'what weapons were used at Columbine,' and 'where to most mass shootings occur.'
Molloy emphasized that the man's decision to carry the rifle in public did not, by itself, spark the decision to take him into custody.
"This case illustrates the very complex nature of balancing an individual's Second Amendment rights with our primary mission to protect and serve all our residents," said Molloy.
Police say they have secured the AR-15.
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