Criminal investigation

Orlando shooter was a security officer and cleared twice by his employer

"We are cooperating fully with all law enforcement authorities, including the FBI, as they conduct their investigations," G4S Secure Solutions said in a statement. "Our thoughts and prayers remain with the victims of this unspeakable tragedy, and their friends and families."

Mateen, 29, killed 49 people and injured dozens more at a gay club in Orlando, Florida, early Sunday morning. The earlier toll of 50, released by officials, had included the gunman.

G4S said that Mateen started working there in September 2007, and that the company ran a background check before it hired him that revealed "revealed nothing of concern."

According to a company spokesman, the check included a criminal record check, prior employment check, education check, social security check, credit report check, drivers license record check, drug test and work references. It also administered an assessment called the security officer profile, which G4S says is meant to determine an individual's potential as security officer.

Florida state records show that Mateen was a licensed security officer.

The background check also included a psychological evaluation, according to G4S. Specifically, the company gave him something called the MMPI -- Minnesota Multiphasic Personality Inventory Test -- which the company describes as an "in-depth, industry-standard test."