By Letitia Stein and Jarrett Renshaw
ORLANDO, Fla. (Reuters) - The man who killed 49 people at a gay nightclub in Florida appears to have acted alone, without direction from the Islamist militant groups he voiced sympathy for, authorities said as they investigated the worst mass shooting in modern U.S. history.
Federal law enforcement officials said the 29-year-old gunman, Omar Mateen, who worked as a private security guard at a gated retirement community, seemed to have been largely inspired by radical ideology he was exposed to over the internet.
President Barack Obama on Monday called Mateen, a U.S. citizen born in New York to Afghan immigrant parents, an apparent example of "homegrown extremism."
The streets leading up to Pulse nightclub in Orlando remained a barricaded crime scene on Tuesday morning. Road closures began right outside the nearby trauma hospital, Orlando Health, where surgeons were due to brief reporters on the condition of the people wounded in Sunday's shooting.
Mourners have laid flower bouquets and set up wreaths near the hospital entrance. A flower bed behind the impromptu memorial was lined with Puerto Rican flags, recognizing the heritage of many of the victims, along with a single American flag.
People who knew Mateen and public records painted a picture of him as a troubled loner who harbored a fierce temper and violent streak, as well as aspirations for a career in law enforcement.
Mateen was shot dead by police who stormed the nightclub before dawn on Sunday, ending a bloody three-hour siege that began when the killer burst into the venue and opened fire with an assault-style rifle and handgun.
The carnage unfolded during a Latin music night at the club, which was crowded with more than 300 patrons. Many of the 49 people killed were Hispanic, more than half of them of Puerto Rican origin. Fifty-three people were wounded.
In the midst of his rampage, Mateen placed a series of calls to emergency 911 dispatchers in which he pledged loyalty to the leader of Islamic State, Abu Bakr al-Baghdadi, whose organization controls large swaths of Iraq and Syria.
He also claimed solidarity in those calls with the ethnic Chechen brothers who carried out the 2013 Boston Marathon bombing and with a Palestinian-American who became a suicide bomber in Syria for the al Qaeda offshoot known as the Nusra Front, authorities said.
Mateen was interviewed in 2013 and 2014 by the Federal Bureau of Investigation, the first time after co-workers reported that he had made claims of family connections to al Qaeda and membership in the Shi'ite militant group Hezbollah, according to the FBI.
Federal investigators found no evidence connecting him to militant groups, FBI Director James Comey told reporters on Monday, noting contradictions in some of Mateen's claims of allegiance.
Islamic State and the Nusra Front are at odds in Syria's civil war, while al Qaeda and Hezbollah are also bitter enemies.
Preliminary findings in the Orlando investigation point to a case of what experts call self-radicalization, officials said.
"So far, we see no indication that this was a plot directed from outside the United States, and we see no indication that he was part of any kind of network," Comey said. "It's not entirely clear at this point just what terrorist group he aspired to support."
Obama echoed the FBI chief's assessment, saying, "It appears the shooter was inspired by various extremist information that was disseminated over the internet."
Islamic State reiterated on Monday a claim of responsibility, though it offered no signs to indicate coordination with the gunman.
The group also claimed responsibility for an attack in France on Monday in which a suspected Islamist attacker stabbed a French police commander to death and later killed his partner.
Comey said the FBI also was "working to understand what role anti-gay bigotry may have played" in the Orlando attack.
GUN LAWS AND HOMELAND SECURITY
Obama on Sunday denounced the killings as both an act of terror and a hate crime.
The massacre reverberated through the U.S. presidential race, with the presumptive major-party opponents in the Nov. 8 election, Republican Donald Trump and Democrat Hillary Clinton, clashing over how to confront Islamist militants.
Trump proposed suspending immigration to the United States from countries with what he said had a history of terrorism against America, Europe or U.S. allies, while Clinton warned against demonizing Muslims and called for tougher gun safety measures.
Obama is to visit Orlando on Thursday to pay respects to families of the victims. Hundreds of people attended a vigil Monday night in downtown Orlando, a central Florida city that is home to theme parks including the Walt Disney World Resort.
Comey said the FBI closed its earlier investigation of Mateen after 10 months, convinced that his assertions of extremist ties were intended to "freak out" co-workers who he said were harassing him for being a Muslim.
Removal of Mateen from the FBI's watch list at that time permitted him to buy firearms without the FBI being notified, Comey said. Both weapons used in the assault were purchased legally.
The Orlando killings came six months after the massacre of 14 people in San Bernardino, California, by a married couple professing Islamist militant ideologies, raising questions about what the United States can do to detect such attackers before they strike.
More than radical ideology may have been a factor in Mateen's case. His ex-wife, Sitora Yusufiy, described him as mentally unstable.
The global security company GS4S <GFS.L> had employed Mateen since 2007 as an armed guard near his home in the Atlantic coastal town of Fort Pierce, Florida, about 120 miles (190 km) southeast of Orlando.
The company said he cleared two security background checks, once when he was hired and again in 2013.
The gunman's father, Seddique Mateen, said his son betrayed nothing of the violence to come when the two saw each other the day before the killings.
"I didn't notice anything wrong," Seddique Mateen said in an interview. "He was very slick."
(Additional reporting by Barbara Liston in Orlando, Yara Bayoumy in Fort Pierce, Fla. and Zachary Fagenson in Port St. Lucie, Fla.; Writing by Steve Gorman and Scott Malone; Editing by Frances Kerry)