The mental health of a former NFL pro who fatally shot five people, including a prominent South Carolina doctor and his grandchildren, "degraded fast" in recent years following his injured-plagued career, a relative said in a new report.

Lauren Adams, sister of Phillip Adams, who reportedly had his medication taken away by Dr. Robert Lesslie before Wednesday’s killing spree, told USA Today her brother’s mental health had devolved dramatically, saying he became more aggressive than usual.

"His mental health degraded fast and terribly bad," Lauren Adams told the newspaper. "There was unusual behavior. I’m not going to get into all that. We definitely did notice signs of mental illness that was extremely concerning, that was not like we had ever seen."

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Adams said her brother was "struggling with his mental health," but said he showed no indications of being violent.

"He wasn’t a monster," she continued, while acknowledging she had noticed a shift in her brother’s behavior. "His temperament had changed where he was super laid back forever and all of a sudden, he had that temper. You could just tell that something was off."

Adams said her brother’s mental health took a turn for the worse following his NFL career, during which he reportedly had two concussions in a three-game span in 2012 while playing for the Oakland Raiders. He ended his career in Atlanta in 2015 after playing for six teams in six seasons and later returned to South Carolina — having lost interest in the game he once loved, Lauren Adams said.

"He really didn’t want anything to do with football," she said. "He didn’t watch it. If we were watching it, he would leave the room or ask us to turn it off."

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Phillip Adams refused to tell relatives where he lived about 18 months ago, his sister said, before he recently moved back home with his parents. Lauren Adams said she thinks he saw a therapist before retiring from the game and later saw other doctors for mental health issues.

Adams later started neglecting his hygiene and became withdrawn, she said.

"So many people come up to me or call me or text me and ask me, ‘What’s going on with your brother?’" Lauren Adams recalled. "And I’m like, ‘I don’t know.'"

Phillip Adams spoke about applying for disability benefits from the NFL while at a funeral weeks ago, his sister said, but felt he wasn’t getting anywhere.

"And towards the end he felt like they were trying to basically stiff him on money," Lauren Adams said. "He felt like they were just trying to nickel and dime him. I think he got upset about that and that’s kind of where it started, with him kind of feeling like the whole world was against him.’’

Adams would not have been eligible for testing as part of a broad settlement between the NFL and former players for concussion-related injuries because he had not retired by 2014, the Associated Press reported.

South Carolina Rep. Ralph Norman, who was close friends with Lesslie, said Thursday he was told by law enforcement that Lesslie had stopped giving Adams medicine – and "that’s what triggered the killings."

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Adams, 32, forced his way into Lesslie’s home, killing the 70-year-old doctor, his wife and their two grandchildren. He also shot two contractors at the family’s home killing one, before turning the gun on himself, York County Sheriff Kevin Tolson said Thursday.