Former NFL star Aaron Hernandez, who was serving a life sentence for murder and just days ago was found not guilty of a separate double murder, killed himself in his prison cell on Wednesday morning, officials said. He was 27.

The Massachusetts department of corrections said Hernandez was found in his cell just after 3am on Wednesday. Prison guards tried to revive the former New England Patriots tight end, but he was pronounced dead about an hour later in hospital.

Department spokesman Christopher Fallon said Hernandez hanged himself. The state medical examiner’s office has taken custody of the body.

Hernandez had been housed in a single cell in a general population unit at the maximum-security state prison in Shirley, Massachusetts. Fallon said officials had no concern that Hernandez was a suicide risk, and that he would have been transferred to a mental health unit had there been any concern about his wellbeing.

“If he had made any kind of statement, he would have not been in that unit,” Fallon said.

Fallon said he was not aware of any suicide note written by Hernandez, but stressed that an investigation is continuing.

Hernandez was serving a life sentence without parole for the 2013 first-degree murder of his friend Odin Lloyd. Hernandez had a $40m contract with the Patriots but was cut by the team within hours of his arrest. He was acquitted Friday in an unrelated 2012 double murder that prosecutors said was fueled by his anger over a drink spilled at a nightclub.

His death was “a shocking and sad end to a very tragic series of events that has negatively impacted a number of families”, said Bristol County district attorney Thomas Quinn, who prosecuted Hernandez in the Lloyd case.

Dan Gronkowski, the older brother of current Patriots tight end Rob, played with Hernandez in 2011. He said the news was “sad to hear”.

Gronkowski said: “It was Rob, myself and [Aaron]. We all got along and had a good time. We didn’t have any issues with Aaron ever. That was all just a side thing that no one knew what was going on. We didn’t even know that that was even happening. It wasn’t even like we thought something like that was going on. So, it’s just sad to hear that, knowing that you [knew] somebody that has gone through that stuff and chose that route.”

Hernandez’s former agent, Brian Murphy, said he couldn’t believe that Hernandez killed himself, and hinted at another explanation. Murphy said: “Absolutely no chance he took his own life. Chico was not a saint, but my family and I loved him and he would never take his own life.”

Jose Baez, Hernandez’s lawyer, says he intends to conduct his own investigation into Hernandez’s death. Baez said his client’s family is “heartbroken, and determined to find the truth surrounding his untimely death.”

Hernandez, a former University of Florida star, was one of the best tight ends in the NFL at the time of Lloyd’s murder. He entered the league in 2010, and in his second appearance became the youngest player in five decades to surpass 100 receiving yards in a game.

He was Tom Brady’s top target in a narrow Super Bowl XLVI loss to the New York Giants, catching a team-high eight passes for 67 yards and a touchdown.

In 38 career games over three seasons, he had 175 catches for a total of 1,956 yards, a number that would have been much higher if not for series of injuries.

Hernandez’s death comes the same day the Patriots are making their visit to the White House to mark their Super Bowl win earlier this year. Team spokesman Stacey James said the Patriots were aware of Hernandez’s death but didn’t anticipate the club commenting on Wednesday.

Massachusetts state police remain on the scene investigating the death.