According to authorities, dozens of bodies were removed overnight Monday from a popular gay nightclub as investigators tried to piece together what had led to a shooting rampage 24 hours earlier that left 50 people dead, including the gunman, and 53 wounded.

The gunman, identified as Omar Mateen, who was killed by the police at the club early Sunday morning, was indeed an American citizen.

Several of the family members who have not yet received information on the status of their loved ones condition, wait nervously for updates. And those who had already learned that their loved ones had died began to plan for funerals.

Law enforcement authorities said that Mateen, wielding an assault rifle and a pistol, stormed the club and called 911 from inside to declare his allegiance to the Islamic State, the brutal group that has taken over parts of Syria, Iraq and Libya. Mateen had been investigated in the past for possible terrorist ties, but the F.B.I. ultimately found no evidence. Still, he was believed to be on at least one watch list.

 

Hours later, the Islamic State, also known as ISIS or ISIL, claimed responsibility in a statement released over an encrypted phone app used by the group. It stated that the attack “was carried out by an Islamic State fighter,” according to a transcript provided by the SITE Intelligence Group, which tracks jihadist propaganda.

A former co-worker, Daniel Gilroy, said Mateen had talked often about killing people and had voiced hatred of gays, blacks, women and Jews.