A new book released this week ties former Patriots tight end Aaron Hernandez to four murders, including one where he was convicted, a double homicide, and an unsolved case in the Hyde Park neighborhood of Boston.

The book is called 'Aaron Hernandez's Killing Fields: Exposing Untold Murders, Violence, Cover-Ups, and the NFL's Shocking Code of Silence.'

The book's author, Dylan Howard, began his two-year investigation after sitting down with a man named Kyle Kennedy, who was Hernandez's cellmate and lover in prison.

Kennedy also said that he and Hernandez ran the Bloods gang behind bars.

Howard was shown letters sent between the two, and Howard tells ABC 6 "there is no doubting in my mind Kyle Kennedy's credibility."

Howard spoke with ABC 6 via Skype and said his new book changes the way people view the Aaron Hernandez story.

"It paints a very disturbing portrait of a man that was seemingly out of control," he said. "Aaron Hernandez led a twisted double life."

Hernandez was sentenced to life in prison for the 2013 killing of Odin Lloyd in Attleboro but was cleared of a double murder in Boston. 

But according to Kennedy, Hernandez admitted to those killings as well as an unsolved fourth murder.

"Aaron once in a conversation with [Kennedy] told him that he had quote, 'four bodies to his name,'" Howard said. "According to Kyle Kennedy, he admitted that he was guilty of those and lied before the court in order to beat the wrap."

As far as the fourth murder, Howard said he pressed Kennedy hard about the possible identity but Kennedy insisted he did not know.

After the hours-long prison interview, Howard and his team began an investigation where they are certain it could be a man named Jordan Miller.

Miller was killed two weeks before Lloyd, and according to research, Howard believes it was a case of mistaken identity.

"The man who was killed execution-style was Jordan Miller. Now, Jordan Miller bears a striking resemblance to Odin Lloyd," Howard said. "I'm sure there's going to be a significant amount of disbelievers but, unfortunately, this is the cold hard reality of whom Aaron Hernandez was and what Aaron Hernandez did."

The book also explores Hernandez's sexuality, what contributions CTE could have played on Hernandez's life, as well as the criminal justice system and problems in our society, according to Howard.

"Issues as a society that we ought to confront. And that is how an individual is able to get away with these types of crimes simply because he thought he was invincible," Howard said.

Howard tells ABC 6 he handed over his evidence to law enforcement, and was told Miller's murder is still an open case.

The Suffolk County DA's Office did not return a request for comment.