NEW YORK – Hundreds of federal agents and police officers widened their investigation of a potential terrorism plot involving an alleged al-Qaida associate on Wednesday as questions lingered about whether early missteps might have made the chore harder.

Investigators have fanned out in a New York City neighborhood to re-interview "people previously encountered" during previous raids there, and to locate others who know them, according to a law enforcement official familiar with the probe. The effort also includes a review of phone and other records that could link potential suspects to one another or identify new ones.

"Many of the people we've spoken to have been cooperative," said the official, who spoke on condition of anonymity to The Associated Press because the investigation is ongoing.

The official said business owners also are on the list of possible witnesses in a potential homemade-bomb plot. The official declined to identify those businesses, but authorities regularly monitor sales by suppliers of chemicals that could be used in improvised explosives.

Najibullah Zazi, a 24-year-old Denver airport shuttle driver whom authorities have linked to al-Qaida; his father; and Ahmad Wai Afzali, a Queens imam, were charged last weekend with lying to the FBI. Authorities say they found bomb-making instructions on a hard drive on Zazi's laptop but knew of no specific time or place for a possible attack.

The arrests came after the series of high-profile raids of several city apartments in the Queens neighborhood where Zazi had recently visited, and were followed by a flurry of nationwide warnings of possible strikes on transit, sports and entertainment complexes.

A criminal complaint suggests police acting without the FBI's knowledge might have inadvertently blown the surveillance and forced investigators' hand by questioning Afzali — considered a trusted police source in the community — about Zazi and other possible plotters. The imam, it says, turned around and tipped off Zazi by calling him the next day and saying in a recorded conversation, "They asked me about you guys."

The detectives referred to in the recently unsealed criminal complaint work for a division that operates independently from an FBI-run terrorism task force.

When multiple agencies are involved in a probe, law enforcement runs the risk of "someone tipping off someone who shouldn't have been tipped off," said Harry Sandick, a former federal prosecutor now in private practice.

"You often have informants who are working both sides," he said. "That seems to part of what happened here, they trusted this fellow and that trust wasn't well-placed. He couldn't be trusted to keep secrets."

The complaint also suggests that the NYPD and FBI might have spooked Zazi even before the imam's call by towing and searching a rental car he was using on his trip to New York City. In the phone conversation with Afzali, Zazi said the car's disappearance convinced him he was being watched.

"Searching the car and him realizing that it had happened, that may have been a little ham-handed, but they obviously had to realize when they interviewed the imam that it could get back to him," said Larry Bacella, another former federal prosecutor.

Police officials say that their investigators reached out to Afzali only after receiving fresh information from the terrorism task force that a terrorism plot was possibly in progress.

In a joint statement, Police Commissioner Raymond Kelly and Joe Demarest, head of the FBI office in New York, denied reports that the questioning of Afzali and his alleged betrayal had caused a rift between the agencies.

"The FBI and the NYPD work together on joint investigations and side by side in task forces on a daily basis," the statement said. "This collaboration is an essential part of what helps to protect New York City from another terrorist attack."