CEO Shooting Suspect Had 'Manifesto' Against Health Care Companies on Him When He Was Detained: Source

The suspect in the fatal shooting of UnitedHealthcare CEO Brian Thompson had a “manifesto” on his person criticizing healthcare companies when he was detained, a law enforcement source tells PEOPLE.

The man was detained by police on Monday, Dec. 9, after a tipster at a McDonald’s in Altoona, Pa. found him suspicious and phoned authorities. He was allegedly found to be in possession of a gun similar to that used by Thompson’s shooter, plus a silencer as well as a false New Jersey ID police allege he used to check into an Upper West Side hostel where the shooter is believed to have stayed.

According to the source, the name the suspect used on his fake ID was “Mark Rosario.”

Thompson was fatally shot outside the New York Midtown Hilton hotel Wednesday in what police described as a “brazen, targeted attack,” The perpetrator fled the scene on a bicycle and was last seen in Central Park.

Authorities believe the shooter arrived in New York City in late November, taking a bus that originally left from Atlanta, though it’s not clear the suspect got on at that point.

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An alleged motive has not yet been established, but on the bullet casings found at the scene, authorities discovered engravings with the words “deny,” “defend,” and “depose.” That’s similar to a phrase about the insurance industry to describe a strategy of rejecting claims, “delay, deny, defend,” which was used as the title of a 2010 book by Rutgers University professor Jay Feinman.

UnitedHealth Group, the parent company of UnitedHealthcare, has announced plans to increase corporate security in the wake of the shooting, The Guardian reports.