As the search for the gunman who killed UnitedHealthcare CEO Brian Thompson stretched into its sixth day Monday, a former top NYPD official shared confidence that investigators are closing in on an arrest.

“There's not a doubt in my mind that they are going to bring this person to justice,” said Kenneth Corey, the NYPD’s former chief of department, during an interview on “Mornings On 1.”

Corey, who now serves as a senior fellow at the University of Chicago’s Policing Leadership Academy, believes detectives are carefully building a strong case before making an arrest.

“This is a worldwide story. People are seeing those photos. There are people who recognize him,” Corey said. “I believe that detectives most likely have a very strong person of interest that they're looking at, and they're just trying to put together a case.”

Corey said the physical evidence detectives have already discovered will likely include DNA from the alleged killer.

“Once you've got a suspect in custody to do that direct DNA comparison, that's going to nail him down,” Corey said. “The backpack, treasure trove of evidence, even if it is just the jacket and Monopoly money that's been reported in there—certainly DNA is going to help connect him to the scene.”

He said investigators are also reviewing video footage to “account for every minute of those 225 hours that he was in New York City.”

Meanwhile, Corey rejected the idea that the online wave of criticism against health care and insurance companies has complicated the investigation.

“I think the investigation is actually moving very rapidly," he said. "I know that New Yorkers and others would like to see somebody in handcuffs already, but detectives have a job to do.”