SAN DIEGO—Authorities Jan. 3 publicly identified two women and a man who died by gunfire last week in a murder-suicide in a neighborhood near Lake Jennings.

Killed in the shooting at the 13500 block of Interstate 8 Business in Lakeside on Dec. 30 were Kenneth Harrington, 59; his girlfriend, Michelle Mallucci, 60; and her sister, Theresa Schrantz, 59, according to the San Diego County Sheriff’s Department.

Detectives have determined that Harrington—who lived in Lakeside, as did Mallucci—killed the women and then shot himself, sheriff’s Lt. Chris Steffen said.

The deadly gunfire was reported shortly after 11:30 p.m., according to Steffen.

“Upon arrival, deputies learned a [man] might have shot a [woman] after an argument, and both were believed to still be inside the residence,” the lieutenant said.

Sheriff’s personnel surrounded the home, and a SWAT team eventually entered, finding the bodies.

Two minors—Schrantz’s grandchildren—were in the residence during the shooting. They have been reunited with their family in Nevada, where their grandmother also lived, officials said.

It remains unclear what prompted the shooting.

“The motivation and circumstances are still under investigation,” Steffen said Tuesday.