Updated

Without the help of an informant who met repeatedly with four accused homegrown terrorists over the course of a yearlong undercover investigation, their plot to blow up two synagogues in New York City and to shoot down planes at an Air National Guard base would not have been thwarted, federal investigators say.

The informant began working last June with James Cromitie, one of the four Newburgh, N.Y., men arrested Wednesday night as they planted what they believed were real explosives at synagogues in the Bronx, according to the complaint.

Cromitie met with the informant in Newburgh, about 70 miles north of New York, and told him he was upset about the war in Afghanistan because his parents had lived there, according to the complaint.

Cromitie also allegedly said he was angry about the deaths of numerous Muslims in Afghanistan and Pakistan at the hands of U.S. military forces.

RAW DATA: Federal Complaint (pdf).

RAW DATA: U.S. Attorney's Press Release (pdf).

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Cromitie told the informant he wanted to go back to Afghanistan and said he'd go to "paradise" if he died a martyr, according to the complaint. He also allegedly expressed a desire to do "something to America."

In July of 2008, the government witness and Cromitie spoke of the Pakistan-based foreign terror organization called Jaish-e-Mohammed — and the informant told Cromitie he was affiliated with the group, the complaint said.

Cromitie allegedly told the informant that he wanted to join the group to "do jihad."

The government witness and Cromitie began meeting in October at a house in Newburgh that the FBI had equipped with hidden video cameras and audio recorders.

During the gatherings, Cromitie and co-defendants David Williams, Onta Williams and Laguerre Payen discussed their desire to attack targets in New York, including two synagogues a few blocks apart in the Bronx and planes at an Air National Guard base, according to the complaint.

The plot allegedly involved detonating plastic explosives packed into a car outside the Riverdale Temple and the Riverdale Jewish Center, a Reform and an Orthodox synagogue, respectively, and shooting surface-to-air guided missiles at military jets at Stewart Airport in Newburgh.

"This was a very tightly controlled operation," New York City Police Commissioner Raymond Kelly told reporters early Thursday.

All four accused terrorists are U.S. citizens, according to authorities. Cromitie, David Williams and Onta Williams are native-born Americans; Payen was born in Haiti.

Kelly said the men are believed to have met in prison. They had lengthy rap sheets for charges including drug possession and assault.

The link between the informant and the suspects is likely a Newburgh mosque they attended called Masjid al-Ikhlas, or the Islamic Learning Center, according to local reports.

Cromitie allegedly asked the FBI informant to supply surface-to-air guided missiles and bombs for the attack. The witness told him he could provide C-4 plastic explosives, the complaint said.

Instead, he gave the men mock explosives.

Last month, according to the complaint, the four suspects chose the synagogues they wanted to target, and they began conducting surveillance of military planes at the Air National Guard base.

Cromitie and David Williams bought a 9-mm semi-automatic pistol to use during the planned terrorist operations, the complaint said. The two also allegedly traveled to the location where they planned to fire missiles at the military planes.

Early this month, Cromitie, David Williams, Payen and the informant drove together to Stamford, Conn., to pick up what the suspects were told were a surface-to-air guided missile system and three improvised explosive devices (IEDs), according to the complaint.

The informant supplied them with a missile he said he'd obtained from Jaish-e-Mohammed. But it was actually an FBI-made device that wasn't capable of being fired, according to the complaint. He also gave them inert C-4 explosives.

Cromitie, David Williams and Payen allegedly transported the bogus weapons back to Newburgh, where they inspected them and discussed details of the plot with Onta Williams.

The four men were charged with conspiracy to use weapons of mass destruction within the United States and conspiracy to acquire and use anti-aircraft missiles, according to the U.S. attorney's office.

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FOX 5 VIDEO: Update on Foiled Terror Plot.

FOXNews.com's Catherine Donaldson-Evans and The Associated Press contributed to this report.