‘It is imperative we get this right,’ FBI says of Orlando shooting investigation

Reporting from Orlando â€”  As President Obama arrived in central Florida to visit victims’ families Thursday, investigators were still trying to determine what motivated the deadly nightclub shooter, and whether he had help.

Federal prosecutors are utilizing a grand jury to help gather records and other evidence on Omar Mateen, 29, the gunman who opened fire at Pulse nightclub early Sunday, killing 49 and injuring more than 50.

“It is imperative we get this right, and we are committed to staying here for as long as it takes to carefully process this vast crime scene,� FBI Special Agent Ron Hopper said Wednesday.

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Hopper said the FBI has given intelligence bulletins to all nightclubs in the Orlando area, including gay clubs, to advise a heightened sense of awareness. But there is no credible or specific threat of an imminent attack against Orlando or the United States, Hopper said.

The owners of other gay nightclubs have vowed to remain open. Parliament House, another nearby club, planned to stage a Latin night benefit Thursday to aid victims of the Pulse shooting. Pulse was attacked during its weekly Latin night, and most of the victims were Latino.

Mateen opened fire at about 2 a.m. Sunday and retreated to the back of the club, where he holed up for several hours with a group of patrons, shooting some before police broke through a wall at about 5 a.m., rescuing the hostages and shooting Mateen.

Police took action because Mateen had threatened to strap bomb vests to the hostages, Orlando Mayor Buddy Dyer said at a news conference Wednesday.

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During the standoff, Mateen told police negotiators that he planned to put explosive vests on four hostages and place them in corners of the nightclub, Dyer said. People trapped inside using cellphones to contact friends, family and 911 operators also warned that Mateen was talking about bombs, the mayor said.

“We had independent verification of that. We had a lot of information from the inside and they independently were saying, ‘Yes, the bomber is about to put on an explosive vest,’� Dyer said.

Of those wounded in the attack, 28 remained hospitalized Thursday: six in critical condition, three guarded, 14 stable and five reported in fair condition.

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UPDATES:

10:44 a.m.: Updates with Obama’s arrival.

This article was originally posted at 8:30 a.m.