A Cobb County woman never imagined her daughter’s boyfriend would hurt her.

“I knew they bickered a lot, but that was it,” Alyson-Renee Johnson told The Atlanta Journal-Constitution on Tuesday.

But on Monday, investigators believe 38-year-old Paul Sullivan assaulted 27-year-old Leilani Billingsley before he killed her and then himself. The shootings happened at a Cobb convention center where Billingsley worked, according to police.

The shots were fired in the rear parking lot of the Riverside EpiCenter, located on Riverside Parkway near Austell, shortly after 11 a.m., according to Cobb police spokesman Sgt. Wayne Delk. Officers found Billingsley and Sullivan dead from gunshot wounds, Delk said.

“Based on eyewitnesses and video information obtained by detectives at the scene, it was determined that Mr. Sullivan had physically assaulted Ms. Billingsley before shooting her,” Delk said in an emailed statement. “He then turned the handgun on himself and shot himself.”

The domestic-related incident remained under investigation Tuesday.

Johnson said Sullivan had been her daughter’s boyfriend for four years and both lived with her in Austell, along with Billingsley’s 6-year-old daughter, Queen-Archee. Now, Johnson said she has learned her daughter was in an abusive relationship, according to one of Billingsley’s friends.

But Johnson said she found out too late to save her daughter’s life. She hasn’t yet told her granddaughter that her mother won’t be coming home.

“Our hearts go out to the family of our beloved team member, especially the young child,” Christopher Boyd, Riverside EpiCenter general manager, said in an emailed statement Tuesday. “Many of our staff are grieving and our attention now turns to loving and caring for those who remain.”

Funeral arrangements for Billingsley were pending Tuesday. A GoFundMe page was created to assist the family.