Calhoun County Sheriff Matthew Wade says investigators are trying to determine why Tony Parker "decided to destroy his family"

An Alabama man fatally shot his son, daughter, and her fiancé before taking his own life — months after he and his wife separated, police say.

Calhoun County Sheriff Matthew Wade tells PEOPLE deputies were called to the home of Tony Parker at around 1:30 p.m. on Thursday afternoon.

After arriving at Parker’s home, they found the lifeless bodies of his 12-year-old son, his 19-year-old daughter, Heather, and her 20-year-old fiancé, Brandon Roberts, in the front yard. (Authorities did not release the 12-year-old son’s name.)

Parker’s body was found a few miles away, in the parking lot of a convenience store.

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Wade says investigators are still trying to determine what motivated Thursday’s violence.

He says cell phones recovered from the scene will be analyzed to determine if Parker communicated with anyone prior to the killings.

Thursday's crime scene
Credit: CBS42

“His wife separated from him in the last several months and he hadn’t been taking that well,” Wade explains.

Before he committed suicide, Parker apparently called his sister, telling her what he did and what he was about to do, Wade says.

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“This is a wonderful community,” Wade tells PEOPLE. “This man, for whatever reasons, decided to destroy his family, which is heartbreaking on many levels.”

PEOPLE was unable to reach Parker’s wife Friday.