A sketch of defendants Akhror Saidakhmetov (left) and Abdurasul Hasanovich Juraboev in Brooklyn federal court on accusations that they tried to join ISIS. The pair, along with Abror Habibov, face charges of conspiracy to provide material support to terrorists. (Credit: Jane Rosenberg; background: CBS2)

NEW YORK (CBSNewYork/AP) — A fourth suspect was in federal custody and was being questioned late Thursday afternoon, over a possible connection to the Brooklyn Islamic State plot.

Three men were arrested and charged of plotting to help ISIS on Wednesday, and authorities have been looking for other New Yorkers who may have been part of their plot.

The fourth suspect has not been charged but he was being questioned by Immigration and Customs Enforcement agents, sources told CBS2.

Two of the three men already charged, who were arrested in Brooklyn Wednesday, were vocal both online and in personal conversations about their commitment and desire to join the extremists, with one of them speaking of shooting President Barack Obama to “strike fear in the hearts of infidels,” federal authorities said.

The men were among three charged Wednesday with attempt and conspiracy to provide material support to a terrorist organization.

Akhror Saidakhmetov, 19, was arrested at John F. Kennedy Airport, where he was attempting to board a flight to Istanbul with plans to head to Syria, authorities said.

WEB EXTRA: Read the complaint (.pdf)

Another man, 24-year-old Abdurasul Hasanovich Juraboev, had a ticket to travel to Istanbul next month and was arrested in Brooklyn, federal prosecutors said. The two were held without bail after a brief court appearance.

Police Commissioner Bill Bratton said this was the first public case in New York involving possible fighters going to the Islamic State, but he hinted at ongoing investigations.

“This is real,” Bratton said. “This is the concern about the lone wolf, inspired to act without ever going to the Mideast.”

A third defendant, Abror Habibov, 30, is accused of helping fund Saidakhmetov’s efforts. He was ordered held without bail in Florida. If convicted, each faces a maximum of 15 years in prison.

As CBS2 Political Reporter Marcia Kramer reported, Habibov was arrested in Jacksonville, Florida, and federal agents on Thursday were reportedly looking into a string of mobile phone kiosks that he owned in East Coast malls.

Agents were trying to determine whether his profits financed terror.

Farhod Sulton, of the Brooklyn-based Vatandosh Uzbek-American Federation, knew Habibov personally. He said they disagreed over Habibov’s Muslim beliefs.

“We had an argument with the gentleman about the understanding; the way he understands Islam,” Sulton said.

Does that mean that Habibov, of Brighton Beach, Brooklyn, had been radicalized years ago? According to Sulton, the answer is apparently yes.

“The way he understands the things – for example, there are some subjects in Islam people understand in a totally different way,” Sulton said. “Modern Muslims understand differently than conservatives.”

Habibov had moved from Brooklyn a few years ago, and fell out of contact with the borough’s Uzbek community, Sulton said.

“We are a community and we greatly regret that this is happening to our community,” he said Thursday. “These people, if all these allegations are true, they don’t represent our community.”

Sulton said at some point, Habibov stopped coming to Uzbek gatherings and he was reading extremist literature, 1010 WINS’ Al Jones reported.

“I think there were concerns about how he understands Islam,” he said. “He wasn’t a crazy guy, he was just a normal guy.”

According to a federal complaint, Habibov provided funds for Saidakhmetov and Juraboev to buy airline tickets to fly to Turkey and join ISIS.

Authorities said Juraboev first came to the attention of law enforcement in August, when he posted on an Uzbek-language website that propagates the Islamic State ideology.