A Millinocket man was arrested Wednesday night and charged with manslaughter in the death of an infant last year.

State troopers and agents from the Maine Drug Enforcement Agency arrested Jessee Mackin, 33, in Millinocket after he was indicted earlier in the day by a Penobscot County grand jury, said Steve McCausland, spokesman for the Maine Department of Public Safety.

Mackin is charged with the death of 6-month-old Larry Lord Jr., who was the son of Mackin’s girlfriend.

The boy died on May 7, 2015, after being taken to Eastern Maine Medical Center in Bangor by his mother. The boy was unresponsive when he arrived at the hospital.

McCausland said the infant’s death has been under investigation by state police and the MDEA for the past eight months.

Mackin is being held in the Penobscot County Jail and will likely make his first court appearance Thursday or Friday.

McCausland said the baby was the son of Anthony Lord, 35, who triggered a massive manhunt in northern Maine in July when he went on a deadly rampage, killing two men, wounding four people and kidnapping a 21-year-old woman.

At one point, during a high-speed chase, Lord shot at an officer from a stolen pickup truck. During the rampage, Lord stole two vehicles, shot out the windows of his brother’s house and set a barn on fire. Lord was arrested at a home in Houlton.

The 21-year-old kidnapping victim, Brittany Irish, survived the ordeal.