Investigators are still trying to determine why former NFL player Phillip Adams killed five people before taking his own life. Police said that Adams shot two air conditioning technicians outside the home of Dr. Robert Lesslie in Rock Hill, South Carolina. He then forced his way into the house, fatally shooting Dr. Lesslie, his wife, and their two grandchildren, ages five and nine.

One of the technicians survived, but the other was pronounced dead at the scene. Adams was found dead several hours later with a self-inflicted gunshot wound.

York County Sheriff Kevin Tolson said they reached out to researchers at Boston University to have Adams brain examined for signs of chronic traumatic encephalopathy, or CTE. Scientists believe the neurodegenerative disease is caused by repeated head trauma and can cause a variety of symptoms, including mood swings, memory loss, paranoia, suicidal thoughts, and impulsive behavior.

During six seasons in the NFL, Adams played for six teams and dealt with several injuries. In his rookie year, he suffered a gruesome ankle in week 16 and required surgery. His agent told CNN that he suffered two concussions during a three-game period while he was on the Oakland Raiders in 2012.

"I think the football messed him up," Adams' father, Alonzo, told WCNC.

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