Anthony Sabato of West Haven, a long-time “person of interest” in the unsolved murder of a Darien police officer in spring 1981, pled guilty in federal court Monday to unrelated drug charges.

The presence of detectives and officers from Darien, Norwalk and other towns at Sabato’s arraignment on federal charges in March fueled speculation that his new brush with the law might lead to a break in the investigation into the murder of Officer Kenneth Bateman more than 34 years ago.

Sabato pled guilty Monday to conspiracy to distribute cocaine in connection with selling crack to a joint undercover task force earlier this year. On July 1, he pled guilty to a single count of conspiracy to distribute and possess with intent to distribute 280 grams or more of cocaine base.

Sabato, 57, a Stamford native who was living in West Haven, was arrested March 25 at his home along with Miguel Joel Roman, 25, for allegedly arranging to buy two ounces of crack cocaine for $2,000, according to the criminal complaint.

A September sentencing is expected, according to Peter Hull, Sabato’s Hartford-based defense attorney. Hull and Assistant U.S. Attorney Tracey Dayton, the prosecutor, both declined to comment further.

According to the March complaint, Sabato and Roman allegedly made repeated drug deals with undercover officers from the West Haven police department between January and late March to sell narcotics out of Sabato’s residence. The men also attempted to buy a firearm from an undercover officer, according to the complaint.

When sentenced on the charge, he will face a mandatory minimum of 10 years in prison followed by five years of supervised release, according to prosecutors and fines up to $10 million.

Under the plea agreement, Sabato also agreed not to challenge his sentence if it did not exceed 14 years in prison.

Sabato initially faced narcotics charges carrying up to 40 years in prison and $5 million in fines, and a gun charge for attempting to buy a firearm that carried a sentence of up to 20 years in prison and a $250,000 fine.

Darien police tagged Sabato as a person of interest not long after the killing of Bateman early on the morning of May 31, 1981 after Batemen responded to an automatic alarm at the Duchess Patio Restaurant near the Norwalk border. Sabato has a wide-ranging criminal history, including 37 Connecticut arrests for burglary, drugs, weapons and assault charges since 1975.

In 2011, former investigators said Sabato came under scrutiny partly because he was suspected in other burglaries occurring along the Post Road at the time of Bateman’s killing. Sabato was never charged in those break-ins.

He was also never charged in a Stamford house burglary committed sometime before Bateman was shot, during which police believe the gun used to shoot him was stolen, investigators have said. Police contend the slug pulled from Bateman’s body was a unique “wad-cutter” that likely was among the ammunition taken in the Stamford burglary. The gun was never found.

On the morning he was killed, Bateman pulled his cruiser into the parking lot, observed the restaurant’s side door was pried open and called for backup, according to police. When he walked to the other side of the fast-food eatery, Bateman spotted the suspected burglar breaking through a plate-glass door to escape, the police accounts said.

After ordering the suspect to halt, according to witness accounts, at least seven shots were fired, with Bateman emptying his Smith & Wesson revolver.

By the time Bateman fired his last shot, he had fallen to the ground. A .38-caliber slug pierced his neck, severing his carotid artery, voice box and windpipe. He was pronounced dead 90 minutes later at Norwalk Hospital.

Since Sabato’s March arrest, Darien police have declined comment about his long-suspected link to killing Bateman. Darien Police Chief Duane Lovello did not return a call for comment Monday.