Los Angeles ? A man with a semiautomatic rifle opened fire at a church festival Saturday in Los Angeles, wounding his ex-wife and two bystanders before festival-goers grabbed him and held him for police, authorities and a church official said.

Witnesses described a chaotic scene, with people screaming and running for the exit after gunfire rang out on a grassy field where the festival was being set up at the St. John Baptist de la Salle Roman Catholic parish.

“I heard bang, bang, bang, bang. It sounded like balloons popping,” said Jeff Sempelsz, a church volunteer who was setting up a booth when the man started shooting. “I didn’t know what it was but I could see the rifle in his hand.”

Father Robert Milbauer, the parish’s pastor, said a woman injured in the attack was the gunman’s ex-wife. The two have a child who attends the school and had been mired in an ongoing dispute, Ruiz said.

“We believe this is an isolated incident, a domestic-violence dispute,” police Capt. Steven Ruiz said.