The 32-year-old reportedly opened fire on Wednesday in a shooting that left five people dead, including Dr Robert Lesslie, 70, his wife, Barbara Lesslie, 69, and their grandchildren Adah Lesslie, 9, and Noah Lesslie, 5, USA Today reported.
James Lewis, 38, was found dead outside the home, police said he was working for a company focusing on air conditioning, roof, and heating repair.
The former cornerback for teams such as the San Francisco 49ers and the New England Patriots was found dead in his family home, seemingly having taken his own life. He played in the NFL between 2010 and 2015.
The suspect's sister, Lauren Adams, told USA Today: “There was unusual behaviour... We definitely did notice signs of mental illness that was extremely concerning, that was not like we had ever seen… He wasn't a monster. He was struggling with his mental health.''
“His mental health degraded fast and terribly bad”.
Ms Adams said her brother had not been violent, but that he had become more aggressive.
She said: “In conversations, it would escalate to arguments. Normally it would just be a normal conversation. His temperament had changed where he was super laid back forever and all of the sudden he had that temper. You could just tell that something was off."
Ms Adams told USA Today that she thinks that some of his problems with his mental health can be attributed to his NFL days. After having left the sport, he returned to South Carolina where he went to university, playing for South Carolina State.
His sister said that his relationship with the game had taken a turn for the worse.
She said: “He really didn’t want anything to do with football. He didn't watch it. If we were watching it, he would leave the room or ask us to turn it off."
His father Alonzo Adams told WCNC-TV: “I can say he’s a good kid. I think the football messed him up.”
Lauren Adams said her brother would give away his clothes and shoes to children in need.
“He loved mentoring kids," she said. She added that as his state deteriorated around a year and a half ago, and that for a time he would not tell his family where he was living. He recently moved back in with his parents in Rock Hill in the northern parts of the state.
“We wouldn’t hear from him for months. It was totally unlike him. He’s always been a family person,’’ Lauren Adams said.
She thinks he saw a therapist before the end of his football career and saw other doctors for his mental health problems after leaving the sport.
As his health got worse, he distanced himself from people and paid less attention to his hygiene, Ms Adams stated.
She said: “He’s always been into looking nice. Like he’s always been like a ladies man. He stopped dating. It was just a lot things that were part of his character that just disappeared.
“So many people come up to me or call me or text me and ask me, ’What’s going on with your brother?’ And I’m like, 'I don't know.'"
Ms Adams said he had recently spoken about applying for disability benefits from the NFL.
She said: “I know he had been applying for disability and he said they were making it hard for him. And towards the end, he felt like they were trying to basically stiff him on money.
“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.’’
York County Sheriff Kevin Tolson said during a press conference on Thursday: “There’s nothing about this right now that makes sense to any of us.”