New York ? After interrupting what they believed was a terrorist plot on New York City with a series of arrests, authorities have intensified their focus on possible accomplices of the suspected al-Qaida associate at the heart of the case, a law enforcement official said Monday.

The official, who spoke on condition of anonymity because the investigation continues, confirmed that investigators know the identities of at least three people believed to be in on a bombing plot they say might have targeted mass transit in the New York area.

Authorities released a flurry of terrorism warnings for sports complexes, hotels and transit systems even while saying the plot was disrupted before it become an immediate threat. But many questions remain unanswered, including the whereabouts of co-conspirators and whether any may be cooperating with the probe.

There also have been no reports that any of the bomb-making materials have been recovered.

The accomplices are suspected of traveling from New York City to suburban Denver this summer and using stolen credit cards to help Najibullah Zazi stockpile beauty products containing hydrogen peroxide and acetone, which can be key ingredients for homemade bombs, authorities have said.

Before the raids, police detectives showed a source — a Queens imam at a mosque where Zazi had once worshiped — photographs of him and three people considered possible suspects, court papers say. It was unclear whether those three were the same ones suspected of traveling to Denver.

The official who spoke to The Associated Press declined to comment further Monday. Spokesmen James Margolin for the FBI, Edward Mullen for the New York Police Department and Robert Nardoza for the U.S. attorney’s office in Brooklyn declined to discuss the case.