The 30-year-old Muslim man who attempted to execute a Philadelphia police officer on behalf of Islam and the Islamic State may have been part of a larger terror plot, law enforcement agencies warned Monday.

Edward Archer, who on January 7 ambushed police officer Jesse Hartnett, may be a piece in a larger jihadi operation, Fraternal Order of Police President John McNesby said Monday, stating that the threat is “being investigated and taken (as) credible.”

An informant told police Sunday evening that Archer, who had traveled to Saudi Arabia and Egypt in recent months, was “part of a group that consists of three others” and that he was “not the most radical of the four,” according to CBS Philly. “The threat to police is not over,” the person with knowledge of the four-person group added.

“If he was the least radical, he was an urban terrorist,” McNesby commented. “Whether it was Islam, ISIS, whether he was in this group, whatever the hell it is, this guy needs to be, these other three need to be looked at if it is credible, taken off the street and investigated,” he added.

The woman also told police that the four men have been radicalized by a local mosque, listing Masjid Mujahideen in west Philadelphia as Archer’s primary place of worship. She claimed the Imam of the mosque lied about his connections to the shooter.

The Imam of the mosque, Asim Abdur Rashid, has now admitted that Archer attended the mosque, went by the name ‘Abdul Shaheed’ (which translates as Servant Martyr), and was a “frequent member.”

But just days earlier, the Imam “said he did not know Archer and was not aware if he had ever prayed there,” according to Reuters.

The Philadelphia Police Department has ordered all police officers to work with a partner while on duty.

The Federal Bureau of Investigation (FBI) and the Philadelphia Police Department have confirmed they are investigating the witness’s claim.

“The Philadelphia Police Department and Federal Partners take this type of information very seriously, particularly after the recent attack on Officer [Jesse] Hartnett. Therefore, the department along with the [FBI] is actively investigating these allegations in an effort to verify the credibility of the information given,” Philly police said in a statement. “The Philadelphia Police Department has alerted all department personnel of this matter and will continue to have officers work with a partner until further notice.”