Prosecutors have asked the governor’s lawyers about the travel arrangements for three trips, including his February 13 rendezvous with a prostitute at the Mayflower Hotel in Washington. The United States attorney’s office in Manhattan has also asked about the governor’s use of car services during trips to Washington.

The governor’s lawyers have begun consulting with a campaign finance expert who has long worked for Spitzer’s political organisation to see whether campaign money was spent on the trips, including some as recently as last month, a person briefed on the investigation said.

The governor, in the two brief statements he made this week as his political career ended, has not directly addressed the allegations concerning his use of prostitutes. But he has told his aides in recent days that he used prostitutes only in the last eight months and never spent campaign or public money in that regard, according to several of the aides. He reaffirmed that position to his lawyer during a meeting at his Manhattan apartment on Tuesday, others present said.

If campaign money was involved, it would expand the scope of a criminal inquiry, because it is illegal to use campaign money for personal expenses. Spitzer, a Democrat, has championed a campaign finance reform proposal for much of his tenure and often excoriated Republicans, saying their fund-raising practices were responsible for the “haze and smog surrounding the capital.”

Several people involved in the campaign said on Thursday that they did not believe campaign money had been misused. Jonathan Rosen, a spokesman for Spitzer 2010, the governor’s campaign committee, and the Excelsior Committee, his political action committee, said neither organisation had received subpoenas from federal authorities.

One of Spitzer’s lawyers, Michele Hirshman, did not respond to requests for comment.

A person briefed on the inquiry said on Thursday that investigators pursuing the case discovered something last fall that raised suspicions that Spitzer may have used campaign money to pay for transportation or hotel rooms for trysts with prostitutes.

It was not clear what two other trips investigators had requested records for from the campaign. Earlier this week, a person with knowledge of the escort service’s operations said that Spitzer had had an encounter with a prostitute in Dallas, and a law enforcement official said another prostitute had met with Spitzer in Florida during the past several months.

Two people briefed on the investigation said that one of the money laundering laws that prosecutors are trying to determine whether Spitzer broke prohibits “the intent to promote the carrying on of the specified unlawful activity.”

Charles H Grice, a banking expert, said that statute was hardly ever used. “This is extremely arcane stuff,” he said.

A friend of Spitzer’s, who spoke on condition of anonymity, reacted with fury at the news that prosecutors appeared to be widening their inquiry to include money spent on campaign trips that may have involved trysts with prostitutes.

“At some point, this becomes piling on,” the friend said. The friend said that he would be stunned if “a judge or jury would convict a man for something like this. It’s very low grade,” adding, “Why would prosecutors pursue this?”