MILFORD — State police are investigating after a 31-year-old man in Milford police custody died early Sunday.

Milford police said they arrested the unidentified man Saturday afternoon after a traffic stop, where police “discovered that he was the subject of an outstanding arrest warrant,” the department said in a statement Sunday afternoon.

While officers were processing his arrest, the man displayed “signs of medical distress and paramedics were immediately summoned to evaluate his condition,” police said.

The man was taken to the emergency room, where he was under observation by medical staff, police said.

“At approximately 11 PM, after examination and observation by emergency room staff, he was released and taken back to the Police Department holding facility,” Milford police said.

The man was monitored in his cell, authorities said, and at 5 a.m. Sunday he was “found to be unresponsive.”

“Officers performed lifesaving resuscitation measures and immediately summoned paramedics. Upon their arrival, paramedics continued these lifesaving measures and subsequently transported the subject to Milford ER. The male was pronounced deceased at that time by emergency room staff,” the department said.

The Central District Major Crimes Squad of the Connecticut State Police will investigate the death, according to protocol, officials said.

The news comes on the heels of the October death of a 23-year-old man in Stamford police custody.

In that case, Steven Barrier was pronounced dead at the hospital about 85 minutes after he was arrested behind a Home Depot. Video of his arrest shows officers carrying him limp into a cruiser.

Sunday’s death was not the first person to die in Milford police custody. In 2006, four officers there were found to have violated department policy after they Tasered a man suspected of swallowing drugs.

Four officers were suspended for one day over the incident, and two dispatchers were fired after they made insensitive remarks, News 12 Connecticut reported at the time.