FORT PIERCE: The gunman who killed 50 people at an Orlando, Florida, nightclub in the deadliest mass shooting in US history was emotionally and mentally disturbed with a violent temper, yet aspired to be a police officer, his ex-wife said on Sunday.

Sitora Yusufiy, the former spouse of Omar Mateen, 29, identified as the shooter slain by police at the end of Sunday's massacre, also told reporters in a news conference aired on CNN that she was "rescued" by family members from her ex-husband after four months of a stormy marriage that ended in divorce.

He was a body builder and a security guard, a religious man who attended the local mosque and wanted to become a police officer. Mateen had no criminal record, and purchased at least two firearms legally within the last week or so, according to Trevor Velinor of the Bureau of Alcohol, Tobacco and Firearms.

Early Sunday, 29-year-old Omar Mateen opened fire at a gay nightclub in Orlando, leaving 50 people dead and 53 wounded, police said. Mateen was the son of an Afghan immigrant who had a talk show in the United States, the nature of which was not entirely clear: A former Afghan official said the program was pro-Taliban and a former colleague said it was enthusiastically pro-American.

Mateen was peaceful, says imam

He attended evening prayer services at the city's Islamic Center three to four times a week, most recently with his young son, said Imam Syed Shafeeq Rahman.

Although he was not very social, he also showed no signs of violence, Rahman said. He said he last saw Mateen on Friday.

“When he finished prayer he would just leave,” Rahman told The Associated Press. “He would not socialise with anybody. He would be quiet. He would be very peaceful."

"He would pray and his son would play," said Rahman, who has known Mateen since 2003 when he became the imam.

He was also bipolar, Yusufiy, told reporters in Boulder, Colorado.

“He was mentally unstable and mentally ill,” Yusufiy said.

Although records show the couple didn't divorce for two years after the marriage, Yusiufiy said she was actually only with Mateen for four months because he was abusive. She said he would not let her speak to her family and that family members had to come and literally pull her out of his arms.

Yusufiy said he wanted to be a police officer and had applied to the police academy. Mateen was a security guard at the G4S company, which identifies itself on its website as "the leading global integrated security company."

Authorities immediately began investigating whether Sunday's attack was an act of terrorism. A law enforcement official said on condition of anonymity the gunman made a 911 call from the nightclub professing allegiance to the leader of the militant Islamic State (IS), Abu Bakr al-Baghdadi.

Yusufiy said she was “devastated, shocked, started shaking and crying” when she heard about the shooting, but she attributed the violence to Mateen's mental illness, not any alliance with terrorist groups.

Rahman agreed.

“My personal opinion is that this has nothing to do with ISIS,” he said.

Rahman said he knew Mateen and his family since the shooter was a young boy. Playful as a child, he became more serious as an adult, Rahman said.

He spoke both English and Farsi, and was into body building. He was not, as far as the imam could see, someone who would ever commit such a gruesome act of mass violence.

“It was totally unexpected,” Rahman said.

"It must be some kind of psychological problem or anger problem," the imam said, adding that Mateen might have been radicalised on the Internet.

Shooter's father has 'anti-Pakistan' views

Seddique Mir Mateen, the father of the alleged shooter, is a life insurance salesman who started a group in 2010 called Durand Jirga, Inc., according to Qasim Tarin, a businessman from California who was a Durand Jirga board member. The name refers to the Durand line, the long disputed border between Afghanistan and Pakistan.

Tarin said Seddique Mir Mateen had a television show on which they discussed issues facing Afghanistan. "It's shocking," he said about the shooting. "(Omar Mateen's) father loves this country."

Some of Seddique Mir Mateen's shows were taped and later posted on YouTube. During one episode, a sign in the background read: “Long live the USA! Long live Afghanistan. ... Afghans are the best friends to the USA."

But a former Afghan official said the "Durand Jirga Show" appears on Payam-i-Afghan, a California-based channel that supports ethnic solidarity with the Afghan Taliban, which are mostly Pashtun.

Omar Khatab, the owner of the California-based satellite channel Payam-i-Afghan, said Seddique Mateen would show up at his studio in Canoga Park, California, "three or four times a year" to tape his shows.

"He'd talk for about two to three hours," Khatab said in a phone interview. "He'd buy his own time and come here and broadcast and leave within a day."

Viewers from Pashtun communities in the United States regularly call in to the channel to espouse support for Pashtun domination of Afghanistan over the nation's minorities, including Hazaras, Tajiks and Uzbeks, the official said.

The "Durand Jirga Show" expresses support for the Taliban, has an anti-Pakistan slant, complains about foreigners in Afghanistan and criticizes US actions there, the official said.

Khatab also said Seddique Mateen's political views were largely anti-Pakistan. A YouTube channel under Mateen's name had more than 100 videos posted between 2012 and 2015.

One of the videos refers to the "killer ISI" ─ Inter-Services Intelligence ─ and says the agency is the "creator and father of the world's terrorism."

Seddique Mir Mateen lavished praise on current Afghan President Ashraf Ghani when he appeared on the show in January 2014, but he has since denounced the Ghani government, according to the official, who said that on Saturday, Seddique Mateen appeared on the show dressed in military fatigues and used his program to criticize the current Afghan government.

"I wish a hero one day removes Ashraf Ghani's turban and slaps this crazy man," he said in the video. "This traitor has rolled up his sleeves to destroy our country."

He also announced on that show that he would run in the next Afghan presidential election, said the official, who spoke only on condition of anonymity because he did not want to be linked to coverage of the shooting.

'He talked of killing people'

In 2013, Omar Mateen made inflammatory comments to co-workers, and he was interviewed twice, FBI agent Ronald Hopper said. He called those interviews inconclusive. In 2014, Hopper said, officials found that Mateen had ties to an American suicide bomber. He described the contact as minimal, saying it did not constitute a threat at the time.

A former colleague at G4S, where Mateen worked as a security guard, told FloridaToday he left his job because Mateen stalked him with dozens of text messages a day and created a toxic environment at work with frequently homophobic and racist comments which went unaddressed by the employer.

"I quit because everything he said was toxic," Gilroy said Sunday, "and the company wouldn't do anything. This guy was unhinged and unstable. He talked of killing people."

Another former colleague from 2004, however, expressed shock on Facebook. Samuel King, an openly gay drag queen, said Mateen was a friend who never discussed religion and was not homophobic in the least.

“He was a jokester and at the time didn’t have an issue with the LGBT community. He might’ve even sat down at the bar and had a drink and laughed with the bartenders, knowing that they were lesbians,” wrote King.