... Officials Say (UPDATE)

EXCLUSIVE

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Adrian Robinson Jr. -- the 25-year-old ex-NFL linebacker -- committed suicide by hanging on Saturday ... officials tell TMZ Sports

A rep for the Harrisburg Police Dept. told us over email that Robinson had been killed in a shooting. But that wasn't the case. 

We spoke with Jeff Moran of the Philadelphia Medical Examiner's Office who tells us, "The manner and cause of death was suicide by hanging."

Robinson -- who played for the Steelers and the Broncos -- is survived by his young daughter Avery Marie.

Story developing ...