The Fairfield man who brought guns to the University of New Haven in 2013, triggering a four-hour lockdown at the campus and nearby schools, was charged Monday with trespassing on Fairfield school property.

William Dong, 24, of Stratfield Road, was charged with first-degree criminal trespass after the assistant principal at Fairfield Woods Middle School called police just before 5 p.m. Monday to report that Dong was seen riding a Segway down the access driveway between the middle school and Jennings School.

Dong had been warned by police detectives that he was not allowed on any public school property in town on three different occasions, following the incident at UNH, where was a student at the time. He told police on Monday he did not realize the access road was school property, and said he had driven the Segway from Stratfield Road to the People’s United Bank branch on Black Rock Turnpike. However, police said they had found Dong leaving the parking lot of the People’s branch on Stratfield Road, not far from his family home.

Police, however, had warned Dong to stay off school property on Oct. 18, when they said he was spotted on his Segway at Fairfield Warde High School, and again on Oct. 27, when he was seen on Fairfield Woods Middle School property. On Nov. 19, police hand-delivered a letter instructing him to stay away from all public school properties.

Dong did not have any weapons with him, and is prohibited from possessing guns as a part of his federal sentence.

On Dec. 3, 2013, Dong was found at the UNH campus with two handguns in his pockets, 270 rounds of ammunition and a Bushmaster assault rifle left in his car nearby the university. The assault rifle is banned in Connecticut — the same type of weapon used by Adam Lanza in the 2012 massacre at Sandy Hook Elementary School — and was apparently acquired by Dong out of state.

Several weeks before the UNH incident, Dong had visited Fairfield Woods Middle School — which he attended until 2005 before moving on to Fairfield Warde High School — after classes had concluded for the day and talked with a former teacher. He left the school after the meeting without incident, school officials said.

Dong was sentenced in state Superior Court the following December to eight years in prison, suspended after serving two years, and five years of probation on state charges of illegally purchasing an assault weapon banned in Connecticut and other weapons charges. In January of this year, Dong received a federal sentence of five years probation.

A federal court judge also ordered him to seek mental health treatment, and he was banned from owning any guns.

Dong was released after posting a $1,000 bond in regard to the latest charge and is scheduled to appear Dec. 17 at state Superior Court in Bridgeport.