NORTHAMPTON — Police said two men targeted a convicted sex offender downtown Thursday evening, assaulted him and then attempted to steal his belongings.

Chad A. Waterman, 33, who lists his address as the streets of Northampton, pleaded not guilty in Northampton District Court on Friday to unarmed assault with intent to rob, threatening to commit murder, assault and battery and misuse of sex offender registry information.

Waterman approached Paul Chandler, 58, as he smoked a cigarette in front of Haymarket Cafe, 185 Main St., just before 7:30 p.m. Thursday. Police say that’s when Waterman and Tyler Julius, 22, who also lists his address as the streets of Northampton, began to harass Chandler about his known history of sex offenses.

Chandler told police he left the area and walked to the bus stop across the street. The two men followed, and Waterman came up from behind and punched him three times on the left side of his face, according to a police report. Police said Julius stood nearby and watched.

Waterman then attempted to run off with Chandler’s duffle bag, but dropped it while fleeing the scene.

A person who witnessed the alleged assault phoned police. Chandler later identified Waterman and Julius to police, adding that — while he had no previous interactions with Waterman — he had previous dealings with Julius, police said.

It was not immediately clear Friday, based on court filings, whether Julius has appeared in court, though police did charge him with criminal harassment, misuse of sex offender registry information, assault and battery and unarmed assault with intent to rob.

State records also show Chandler was convicted in 1995 of multiple counts of indecent assault and battery on someone older than 14 and rape and abuse of a child.