According to deputies, Myslene Gabriel, Raymond's 25-year-old sister on his father's side, had told investigators less than a week earlier that she was the victim of aggravated battery and that she was three months pregnant.
Authorities found Gabriel's 2-year-old daughter uninjured in another room Monday.
Gabriel's autopsy hasn't been completed, but "there is evidence of foul play and detectives are working the case as a homicide," Manatee County Sheriff's Office stated in a news release.
Deputies had responded to a domestic battery call April 5 at an apartment complex. Gabriel told investigators that her ex-boyfriend, Bryan Stanford, 26, grabbed her face and hit her with an open hand, deputies said.
The tragedy is the latest in a string of them for Raymond, who nearly lost his mother, sisters and his sisters' children three years ago in an attack at the family home in Palmetto, Fla.
Raymond's cousin, who lived next door to Raymond's family, had killed someone in self-defense, and friends of the victim retaliated by throwing Molotov cocktails through the windows of Raymond's childhood home. His mother was home at the time, as was his older sister and her two children and his pregnant younger sister.
"It was situation where they just picked the wrong house," Raymond told the Tribune while noting how the attackers meant to swarm his cousin's home. "And while my mother and sisters were struggling to get out, the assailants or whatever you want to call them started shooting. So they were forced to run back into the house while it was on fire.
"I guess some buddies of mine that were down the street, they came and they ran the guys off. But my older sister, she was shot multiple times and didn't even know it. She was running off adrenaline, trying to keep everybody situated."
According to reports, Nanise Raymond, the older sister, was shot at least four times, including twice in the leg, after two masked gunmen opened fire, but she survived after emergency surgery.
The rest of the Raymonds were unharmed, but the family lost everything in the fire. Raymond's mother, who was disabled, died six months after the fire because of a lung-related illness, although it's unclear if the fire contributed to her death.
The incident changed the path of Mistral Raymond's football career. He was considering scholarship offers from Temple and Central Michigan after junior college but decided to walk on at South Florida to be closer to home. Palmetto is just 45 miles south of Tampa.