U.S. President Barack Obama said Monday there is "no clear evidence" that the shooter who carried out the biggest mass killing in the country's history at a gay nightclub in Orlando, Florida, was directed by an overseas terrorist group.
"It appears the shooter was informed by extremist information disseminated over the internet," Obama told reporters at the White House.
He said the shooter, Omar Saddiqui Mateen, a 29-year-old American Muslim born to Afghan parents, represented a "kind of homegrown extremism that we've been concerned about for a long time."
But, Obama said, "It does appear that at the last minute he announced allegiance" to the Islamic State group in calls to Orlando's 911 emergency line.
Watch: Obama Discusses Orlando Attack
Obama said law enforcement officials are "still at the preliminary stage" of their investigation and that there is still "a lot more that we have to learn."
Federal Bureau of Investigation chief James Comey said, "We're going through the killer's life," including his use of internet.
Patrons of Pulse have claimed to have seen Mateen drinking at the bar multiple times before the shooting. Witnesses have also reported seeing him on gay chat and dating app "Jack'd."
Late Monday, White House spokesman Josh Earnest said Obama will travel to Orlando on Thursday “to pay his respects to victims' families, and to stand in solidarity with the community as they embark on their recovery.”
Weapons Purchased Legally
Obama, speaking the day after 49 people were gunned down at the Pulse nightclub and another 53 were wounded, said the shooter legally bought the weapons used in the attack. He said one of the weapons used in the rampage was "a handgun with a lot of clips."
Authorities said Mateen, who was later killed by police, sprayed round after round at late-night revelers in the club with a semi-automatic rifle.
"It was not difficult for him to obtain these kinds of weapons," said Obama, who has unsuccessfully fought for tighter gun laws in the U.S. "This is going to be something we have to grapple with."
He said the U.S. is "so lax" in the ease with which disturbed people bent on carrying out armed mayhem can purchase weapons.
Authorities in Orlando said they are working on a hundred leads to try to determine if the suspected shooter at a gay nightclub had help in carrying out the attack.
"There may be prosecutions down the road," FBI agent Paul Wysopal told reporters.
WATCH: Witness recalls club shooting
Authorities said that during his attack on the club, Mateen called the Orlando emergency line and vowed fealty to Islamic State and its leader, Abu Bakr al-Baghdadi, and also referenced the 2013 Boston Marathon bombing that killed three people.
But the shooter's father, Seddique Mateen, denied his son's actions had anything to do with Islam.
Father 'didn't know'
"I don't know what happened and I didn't know he had hatred. He went to a gay club for men and women and shot 50 of them with a gun," Seddique Mateen told reporters Monday.
He described his son as "a good son and an educated person." However, he later went on to say, "God will punish those involved in homosexuality," saying it's "not an issue that humans should deal with."
U.S. Attorney Lee Bentley said that others who may have had connections to Mateen are being investigated, but that there is "no reason to believe" the public may be in further danger.
The FBI twice in recent years questioned Mateen about possible connections with terrorist groups but found nothing to warrant any charges.
Theme parks in the Orlando area are, nevertheless, stepping up security in the wake of the attack. Captain Angelo Nieves of the Orange County sheriff's office told the Orlando Sentinel that law enforcement officers at Disney World "were put on alert."
Comey said the agency is trying to determine whether Mateen recently scouted Walt Disney World and other locations as potential targets.
People magazine, citing an unnamed federal law enforcement source, reported that Mateen recently scouted the theme park.
Police ended the early Sunday mayhem at Pulse after three hours, shooting Mateen to death after heavily armed police tactical units raided the club, which calls itself the "hottest gay bar in Orlando."
Orlando Police Chief John Mina said the raid "saved many, many lives." He said one policeman was hit in the head by one of the gunman's shots, but that his Kevlar helmet saved his life.
Officials said two of the gunman's weapons, including a semi-automatic rifle, were found in the club and a third located in his car.
Orlando Mayor Buddy Dyer said officials have identified all but one of the 49 victims and so far have been able to reach half of their families to let them know of the deaths of their loved ones. Florida Governor Rick Scott said many of the victims were residents of Puerto Rico, a U.S. island territory off the southeastern U.S. coast and a short flight from Florida.
As authorities continue to sort through the horrific, bloody scene at the club, some survivors are beginning to recount their escape from the gunman's onslaught.
WATCH: Gay Men's Chorus of Washington Sings at White House Vigil
"I crawled my way outside the back exit," Christopher Hansen told CNN. "I was zig-zagging my way," hearing gunfire as he left the chaotic scene — "boom, boom, boom."
Another man at the club, Jon Alamo, said he spotted the gunman and feared for his life.
'I'm going to die'
"My first thought was, 'Oh my God, I'm going to die,''' Alamo said. "I was praying to God that I would live to see another day. I couldn't believe this was happening.
"He was holding a big weapon," Alamo said. "He had a white shirt and he was holding the weapon. ... You ever seen how Marine guys hold big weapons, shooting from left to right? That's how he was shooting at people."
Alamo said he escaped by running to one of the club's smaller dance rooms, along with others who fled the gunman's fury by rushing to an area where club workers had knocked down a wooden fence to create an escape route.
Vigils and marches are being held around the country Monday and later this week. Obama ordered U.S. flags to be flown at half-staff in memory of the victims.