Under the shroud of darkness, a man drives his family to the edge of a Phoenix-area lake, grainy surveillance video shows.

After he gets out to survey the lakefront, he gets back into the SUV. The vehicle races over an embankment and flips over, trapping Glenn Baxter and his young, estranged family upside down in the water. Despite the efforts of fishermen and police diving in to pull them out of the water, there were no survivors.

Tempe police say what the 27-year-old Baxter did was deliberate. They’re investigating it as a murder-suicide.

The early Sunday morning incident killed 25-year-old mom Danica Baxter, a 3-year-old son Reighn, a 2-year-old son Nazyiah and a 1-year-old daughter Zariyah, along with Glenn Baxter.

Danica Baxter’s grandfather, George Britt, said Glenn Baxter had anger issues. The couple wasn’t living together, he told CNN affiliate KTVK.

Britt’s wife, Crysel Woods, said Danica was trying to move on, but Glenn had other ideas.

“He had been threatening her about how he would kill the whole family if she ever left him,” she told the affiliate.

“I think it was a murder-suicide,” Britt said, concurring with police. “My heart is sick. It’s sick. It’s sick. It’s going to be a while before my heart get back right.”

Tempe police will continue their investigation, but for the man who lost a granddaughter and three of his great-grandchildren, the reality is already clear.

“He took part of me when he took them,” Britt said. “He really took all of me.”