FILE - This file photo released on Sept. 20, 2012 by the Arapahoe County Sheriff's Office shows Colorado movie theater shooter James Holmes. While on the stand, Robert Holmes testified that his son came home from winter break from graduate school in 2011, several months before the shooting, and was making odd facial expressions which his parents had not seen in him before. AP Photo/Arapahoe County Sheriff via AP

Centennial, Colorado - The father of Colorado's movie massacre gunman told his murder trial on Wednesday how he was quizzed at an airport just hours after the rampage by FBI agents who he said were interested in whether his son might be a “terrorist.”

“They were interested in whether he had a history of violence, which he didn't, and they were interested, I thought, in whether he was a terrorist,” Bob Holmes said. “I told them I didn't think there was any chance he was a terrorist.”

Bob Holmes testified for a second day during the penalty phase of the proceedings. The jury has already convicted his 27-year-old son James of all counts related to the July 20, 2012 mass shooting. It must now decide whether he should be executed or serve life in prison for killing 12 people and wounding 70 at a midnight screening of a Batman film.

The defense is trying to convince the nine women and three men on the jury that mitigating factors including severe mental illness mean he should be spared the death penalty for the mass shooting at a multiplex in the Denver suburb of Aurora.

Concluding his cross-examination of Bob Holmes, District Attorney George Brauchler asked him if he remembered telling FBI agents that when he last spoke to his son in Colorado by phone on July 4, James had “seemed good and happy.”

The gunman's father said he had learned of the massacre only hours earlier, and that he was approached by the two agents as he waited at an airport for a flight to Denver. They took him to a small conference room below the terminal where they questioned him about James, he said.

Defense attorney Tamara Brady asked him what frame of mind he had been in, and whether he had been worried about his son and the rest of his family.

“(I was) in turmoil,” he replied. “I could have said he was happy. What I meant was he didn't give any inkling he was homicidal or stressed or anything, at least to us, on July 4.”

His wife, Arlene, is expected to testify later on Wednesday, as the defense tries to convince the that any mitigating factors outweigh the aggravating factors they ruled on last week.

Prosecutors have portrayed Holmes as a calculating killer who hid his detailed preparations for the attack, including from his parents back home in the San Diego area.