A Boston man stumbled through a drug investigation and into his own arrest Sunday in Charlestown.

Officers originally spotted a man they suspected to be involved with drugs at the Community College T station and watched him as he met with another man in the company of a young child, who the man later identified as his daughter, according to a report.

The men and the child walked together across the footbridge, then parted afterward. Soon after, officers stopped and confronted both men.

One group of officers caught up with the man who had been with the child at Thompson Square. A detective saw him swallow, a report said, and police advised him of his rights.

During the confrontation, the report said, the man became agitated and jammed his hand into his jacket pocket “in a threatening manner.”

In response, and officer grabbed the man’s wrist and struck him with his knee. In the pocket, the officer found a cigarette package that was returned to the suspect’s possession upon his release.

Officers stopped the second man near the corner of Main Street and Green Street. He told police that he had just gotten off the train, which officers had observed to be incorrect. He also denied meeting with anyone, and officers found a prescription bottle and pills in the man’s possession.

During the course of the conversation, officers handcuffed the man “for officer safety,” the report said.

While officers waited to hear the result of the other officers’ inquiry, two men walked by and greeted the suspect in handcuffs, asking him “what’s up?”

“I’m in handcuffs,” the suspect responded.

One of the men, Joseph DeAngelo of 81A West Dedham Street in Boston, apparently didn’t hear the response and offered to sell drugs.

“I got Percs and ABGs, you guys want any?” DeAngelo said.

The suspect in handcuffs mouthed the word “cops,” but DeAngelow failed to receive the warning.

An officer turned to him and offered to buy a pill. As the officer pulled money from his wallet, the other man finally received the warning.

“You’re cops, aren’t you?” he said.

The officers denied being police. The man then backed away, and officers put him into handcuffs.

Officers reported finding a total of 44 pills in the Deangelo’s possession. He was charged with possession of both class A and B substances with the intention to distribute them.

The other men were released.