Two days after a Philadelphia police officer was shot by a man who said he had pledged loyalty to the Islamic State, the city’s police and the FBI are investigating a tip that the man was part of a group with radical beliefs that might still pose a threat.

According to a statement from the Philadelphia Police Department on Sunday, a citizen stopped a Philadelphia officer on the street on Saturday night to warn that the alleged gunman, Edward Archer, was part of a larger group.

ABC News, which obtained the police report from Saturday night, reported that the unnamed tipster was a woman. She told the police that the man involved in Thursday’s shooting (Archer is not mentioned by name) is not the most radical of his group of four people, and that the threat to police is not over.

Authorities in Philadelphia say that Archer shot Officer Jesse Hartnett multiple times in an assassination attempt in West Philadelphia late Thursday night. Hartnett, who is now in the hospital in stable condition, was able to return fire and injure his attacker.

After apprehending Archer, a 30-year-old from Yeadon, Pa., police say that he told them he had carried out the attack in the name of Islam.

“He stated that he pledges his allegiance to the Islamic State, he follows Allah, and that is the reason he was called upon to do this,” Capt. James Clark said at Friday’s news conference. “He kept on echoing those sentiments, and he wouldn’t give us anything more than that.”

The female tipster Saturday told police that Archer had attended a mosque in Philadelphia but became more radical after switching to another mosque nearby.

A Philadelphia Police Department Announcement:Last night a Philadelphia Police Officer was stopped by a citizen on the…

Posted by Philadelphia Police Department on Sunday, January 10, 2016

Archer has been charged with attempted murder, aggravated assault, assault on a law enforcement officer, recklessly endangering another person, possession of an instrument of crime, violation of uniform firearms act and related offenses, Philadelphia police told ABC.

The woman’s tip from Saturday night could not immediately be corroborated, police told ABC. But they added that the tip is not isolated and that they and the FBI will be looking into it and similar tips as they investigate the incident.

The shooting in Philadelphia comes during a time of increased anxiety about terrorism in the wake of the December mass shooting that killed 14 people in San Bernardino, Calif. The massacre was later labeled a terror attack, and authorities say that the female shooter later went on Facebook to announce that she and the other gunman pledged allegiance to the head of the Islamic State.

Richard Ross Jr., the city’s police commissioner, said Friday that Archer had carried out the attack with a stolen gun and was targeting police. Archer allegedly told officers that he believed Philadelphia police were enforcing laws contrary to the Koran.

An FBI spokesperson also told The Washington Post that the agency is looking into trips that Archer had taken to Saudi Arabia in 2011 and to Egypt in 2012.

It is not clear how strong a connection, if any, Archer may have had to the Islamic State. J.M. Berger, an expert on terrorism and ­co-author of “ISIS: The State of Terror,” told The Post on Friday that this might fit the pattern of recent attacks in which people invoke the group without formal ties or exposure.

“This is the model we’ve seen for ISIS over the last year or so,” Berger said, using an acronym for the extremist group. “People, sometimes with very loose affiliation or no affiliation with the group, acting out in its name.”

Archer’s mother, Valerie Holliday, said that her son was a devout Muslim who had suffered head injuries.

“He’s been acting kind of strange lately,” she told the Philadelphia Inquirer. “He’s been talking to himself. … He’s been hearing voices in his head. We asked him to get medical help.”

Court records show that Archer was charged with aggravated assault, terrorist threats and other offenses for an incident in 2012. He pleaded guilty last year to charges of simple assault and carrying a firearm without a license.