LOWELL — All criminal charges against Ipswich Fire Chief Gregory Gagnon, a Dracut resident who was accused last year of assaulting and strangling his wife, were dropped Monday after Gagnon’s wife asserted her right not to testify, according to court filings.

Gagnon, 42, was scheduled to go on trial Monday on charges of strangulation, assault with a dangerous weapon, intimidation of a witness and assault and battery on a family or household member.

But prior to the start of the trial, Assistant District Attorney Suzanne Kontz, who was handling the case, filed notifications that the charges were being dropped because Gagnon’s wife asserted her marital privilege to not testify against her husband.

“Due to that assertion and subsequent unavailability of that necessary witness, the commonwealth has insufficient evidence and therefore is unable to proceed with the trial as to these charges at this time,” Kontz wrote in a court filing.

Kontz wrote that prosecutors reserve their right to pursue the charges in the future should circumstances change.

Gagnon, who spent 18 years as a highly-regarded Dracut firefighter before being hired as chief in Ipswich in 2014, has been on leave from his job in Ipswich since the charges were filed in mid-September.

Ipswich Town Manager Robin Crosbie said Gagnon remains on leave, and has agreed to part ways with the town this month.

Gagnon was accused of strangling his wife until she had difficulty breathing about a year ago, though his wife did not immediately report that incident to police, according to police reports.

In early September, he allegedly put his Glock handgun on a bed in front of his wife of 17-years and told her that if she didn’t leave the couple’s Dracut home “he would shoot her in the head so her brains would be splattered on the wall,” according to a police report.

When his wife threatened to call police, Gagnon said “guns will be blazing when they get here,” and suggested that both he and his wife would end up dead, according to a police report.

His wife then left the couple’s home, but returned later when Gagnon called her and said she could sleep in a spare room, according to a police report. But when the wife returned, Gagnon pinned her against a wall with a mattress and told her he wanted to slap her, according to a police report.

Gagnon’s firearms were confiscated by police as a result of the incidents, according to police reports, which indicate Gagnon was suicidal at one point in the past.

Gagnon was released following his arraignment on the charges, but agreed to a court order that required him to attend counseling at the Brattleboro Mental Health Center in Brattleboro, Vt.

Court filings in the case indicate Gagnon completed his counseling there in October, and has been in aftercare programs and counseling since.

Court filings show that Gagnon and his wife were attending joint counseling, and that they sought the court’s permission to communicate about issues involving their children’s care and counseling.

Gagnon’s attorney, Christina DeBernardis, said Monday that her client and his wife request their privacy as they get on with their lives.

“My client is pleased that the case is closed and he’s anxious to move forward,” DeBernardis said.

Police reports connected to the case indicate Gagnon struggled with stress after taking the chief’s job in Ipswich, where there have been numerous issues between administrators and the firefighter’s union both before and since his arrival.

Police reports filed in the case indicated that taking the job cost Gagnon former friends since he found himself on a new side of union issues.

Gagnon’s wife told police her husband’s life “became very stressful” once he became fire chief, according to police reports.

Follow Robert Mills on Twitter @Robert_Mills