A story recently published by the Daily Caller website said Melgen flew Menendez to the Dominican Republic and arranged trysts for him with prostitutes, including some alleged to be under age.
It was unclear Wednesday whether the FBI raid centered on Melgen's finances, the prostitution allegations, or anything else related to Menendez. FBI spokesmen would neither confirm nor deny that the agency was investigating the senator.
A nonpartisan Washington watchdog group that often criticizes members of Congress said it had checked into the prostitution allegations and was unconvinced. Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington (CREW), said months of e-mail exchanges last year with the only publicly named source to tie Menendez to prostitutes left her "increasingly skeptical" of the allegations.
Her group "took the allegations very seriously, but there is something very suspicious about a source who repeatedly and for months refused to speak by phone to either us, other news outlets, or the FBI," Sloan told The Inquirer.
The group traded e-mails with the source, who gave his name as Peter Williams, while looking into his claims, but the accuser repeatedly refused to meet or speak with investigators from CREW or an ABC News reporter looking into the matter, she said.
Williams also exchanged e-mails with the FBI over several months but appears to have refused to meet in person with an agent, according to records posted online that the Miami Herald said it had verified.
The scrutiny of Menendez, 59, comes as he is poised to play a key role in the debate over immigration reform and to become chairman of the influential Foreign Relations Committee, the post Sen. John Kerry (D., Mass.) is leaving to become secretary of state.
FBI agents took items from Melgen's medical offices in several vans late Tuesday, the Herald reported. The FBI would confirm only that "we are conducting law enforcement activity in the general vicinity of 2521 Metrocentre Blvd.," the address of one of Melgen's offices. "No further comment/information at this time."
Melgen has an outstanding $11.1 million IRS lien for taxes owed from 2006 to 2009, and a previous IRS lien for $6.2 million that was released in 2011, the Herald reported.
Sloan, of CREW, said she looked into the allegations about Menendez and prostitutes in the spring, but the accuser would communicate only by e-mail. She said it was odd he would come forward with allegations from 2008 in the midst of Menendez's reelection campaign last year.
"If you really wanted Menendez brought to justice, you would be cooperating," Sloan said.
Reporters who called her about the allegations were prodded by Republican operatives, Sloan said. She eventually turned over the information to ABC News and the FBI.
A series of e-mails published online Jan. 24 show Williams corresponded with the FBI for roughly five months, laying out allegations but refusing repeated requests to speak by phone or in person. The e-mails are real, the Herald reported. It's unclear who created the website where they appeared.
In one of the e-mails, an FBI agent says most of Williams' information is true, but he does not specify which information.
The accuser's name has a political ring to it. New Jersey Democrat Harrison "Pete" Williams was forced to resign from the U.S. Senate in 1982 after his conviction on bribery and conspiracy charges in the Abscam scandal.
Menendez's political fund-raising and some of his other actions have come under scrutiny before, though he has never been charged with a crime. When he ran for Senate in 2006, federal investigators looked into an arrangement in which he leased space to a nonprofit that was getting federal funding. And in 2004, he was found to be one of many politicians who received illegal donations from Democratic fund-raiser Charles Kushner. Kushner later went to jail for cheating on his taxes and intimidating people who cooperated with investigators.
On Tuesday, a North Jersey man pleaded guilty to making $21,400 in illegal contributions to Menendez. That investigation appeared to be unrelated to the one in Florida, which centered on Melgen's offices.
Melgen and his relatives have given $33,200 to Menendez's campaigns and $125,400 to Democratic campaign arms in the Senate, House, and New Jersey, public records show, including $60,400 in 2009 to the Democrats' national Senate campaign committee, then headed by Menendez.
"Dr. Melgen has been a friend and political supporter of Sen. Menendez for many years," Menendez's office said. "Menendez has traveled on Dr. Melgen's plane on three occasions, all of which have been paid for and reported appropriately."
Menendez did not pay for two of the flights until two years later, after New Jersey Republicans raised questions about the trips with the Senate Ethics Committee, the Newark (N.J.) Star-Ledger reported Wednesday. The senator repaid $58,500 on Jan. 4 for two flights he had taken to the Dominican Republic in 2010, the newspaper reported.
The Daily Caller has kept the prostitution angle alive since the fall while noting that the practice is legal in the Dominican Republic. Shortly before the Nov. 6 election - in which Menendez easily defeated his Republican challenger, State Sen. Joseph Kyrillos - the site posted videotape of two women who said they were prostitutes and claimed they had sex with Menendez. Their faces were blurred so as to make them unidentifiable.
Last week, the site reported on the e-mails between Williams and an FBI agent. The last e-mail exchange posted online was from late December. Reached by phone earlier this week, the agent, Regino Chavez, declined to comment.
Williams did not respond to requests for comment from The Inquirer this week. Efforts to reach Melgen Wednesday were not successful.
Contact Jonathan Tamari at email@example.com or follow on Twitter @JonathanTamari. Read his blog, "Capitol Inq," at www.philly.com/CapitolInq.