John Comparetto, 56, was attending the meeting of 300 officers when he was allegedly held up at gunpoint in the men's toilets, NY Daily News reports.
He gave up his money and mobile phone but then he and some colleagues gave chase as the suspect tried to flee in a taxi.
Mr Comparetto stopped the taxi at gunpoint with his fellow officers, who then arrested a 19-year-old man near Harrisburg, Pennsylvania.
"This is probably the dumbest guy in the state of Pennsylvania," Mr Comparetto said. "He actually walked past a great, big poster that said, 'WELCOME NARCOTICS OFFICERS.'"
When a reporter asked the suspect for a comment as he was led out of the court, he said, "I'm smooth."
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