The United States' anti-terror strategy, especially in tackling "lone-wolf" attacks, and gun control policies have come under fresh scrutiny after it emerged that the gunman responsible for the deadliest mass shooting in US history had previously been cleared of militant links.
Omar Mateen, 29, whose shooting spree at a gay nightclub in Orlando on Sunday left 49 dead, had been interviewed by the US Federal Bureau of Investigation on two occasions, the most recent in 2014. But the FBI found no evidence to hold him - showing how difficult it is to detect these lone attackers.
Even though the Islamic State in Iraq and Syria (ISIS) claimed responsibility for the mass shooting and Omar had pledged allegiance to ISIS during a 911 call as he began his attack, US officials stressed it was still too early to tell if he actually had any contact with the militant group.
As the US authorities continued their investigation into Omar and his motive, condolences flowed in from across the world.
Prime Minister Lee Hsien Loong offered his condolences on behalf of the Government and people of Singapore, and said he was "deeply shocked and saddened" by the tragedy. Singapore, which has grown increasingly wary of lone-wolf attacks, has raised the terror alert to its highest level and stepped up security measures at key facilities.
Alert levels were also raised on the West Coast of the US in the aftermath of the Orlando shooting after a 20-year-old was arrested in California with a cache of weapons and bomb-making materials.
A debate was also reignited about why Omar, a man the FBI suspected to have ISIS links, was able to buy a handgun, an assault rifle and thousands of rounds of ammunition.
US President Barack Obama reiterated his call for common sense gun control measures.
"We have to decide if that's the kind of country we want to be. And to actively do nothing is a decision as well," he said in a televised address.
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