Omar Mateen, 29, attended evening prayers three or four times a week at the Islamic Center of Fort Pierce, bringing his son who is about four or five years old, the mosque's imam said.
US Muslim leader condemns Orlando attack, slams extremists
"He would pray and his son would play," said Syed Shafeeq Rahman, who has known Mateen since 2003 when he became the imam.
Mateen did not socialise, leaving when services ended.
He didn't talk but would smile and shake hands, Rahman said.
The imam said it was "unbelievable" that a heavily-armed Mateen carried out a rampage at a gay club in Orlando, killing 50 people and wounding 53.
It was the deadliest terror attack in the United States since September 11, 2001.
Authorities said Mateen apparently called 911 before the massacre and pledged allegiance to the Islamic State group.
He was mentally unstable, says ex-wife of suspected Orlando shooter
"I never expected this," Rahman said, holding a Holy Quran in his hand as he spoke with reporters. "We teach peace and justice."
"It must be some kind of psychological problem or anger problem," the imam said, adding that Mateen might have been radicalizsed on the Internet.
Mateen's parents regularly attend services at the mosque and his father works in life insurance, the imam said.
Deadly rampage: Orlando hit by worst shooting in US history
Rahman said he was concerned about the safety of the mosque, located on a quiet residential street in the small coastal city of Fort Pierce.
"The people who are bad people look like us, and that's a problem," he said.
COMMENTS (9)
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ