Thomas Kim's previous court appearances were canceled because of a medical issue.
He is charged with murder in the shooting death of Long Beach FD Capt. David Rosa, as well as the attempted murder of another firefighter and a resident of the complex.
Rosa, 45, was fatally shot while searching for victims in an explosion at the senior living facility. Kim is accused of triggering the explosion designed to kill his upstairs neighbor and then shooting firefighters who responded to the blaze.
Rosa was a 17-year veteran of the Long Beach Fire Department. He leaves behind his wife and two children.
Kim's arraignment was delayed until Aug. 15 due to medical issues and not being able to communicate with an attorney.
Several Long Beach firefighters attended the hearing Monday. Deputy Chief Rich Brandt said every day is difficult for Rosa's colleagues. "I know Dave is looking upon us and knows that we're here to protect him and his family and the world we live in," Brandt said.
The firefighters said they will be back in court at Kim's Aug. 15 hearing to show their support for Rosa's family.
"We'll continue to do what we have to do, and that's what Capt. Rosa would want, and that's what we're going to do, and we'll continue to support him and his family and the rest of the fire service throughout," said Brandt.
City News Service contributed to this report.