A senior U.S. Navy criminal investigator has pleaded guilty to bribery charges stemming from a multimillion dollar fraud probe targeting an Asian defense contractor.

John Beliveau II entered his guilty plea in federal court Tuesday in San Diego.

Beliveau acknowledged keeping Singapore-based contractor Leonard Glenn Francis abreast of the investigation in exchange for trips and prostitution services. Francis has pleaded not guilty in the case.

Beliveau could face a maximum sentence of 20 years.

The conviction is a first for federal prosecutors in the massive scandal that has ensnared six Navy officials so far and could lead to an expansion of the probe if Beliveau cooperates with authorities as part of his plea agreement.

His attorney and prosecutors declined to say whether Beliveau had agreed to help.

Prosecutors say Francis, 49, the CEO of Glenn Defense Marine Asia Ltd., or GDMA, overbilled the Navy by at least $20 million. They said the scheme included giving bribes to Navy officers who would provide Leonard with confidential ship route information or direct the movement of Navy vessels to Asian ports with lax oversight so the company could inflate costs and invent tariffs by using phony port authorities.

“This isn’t only bad news for Leonard Glenn Francis, but I suspect there are a number of yet unnamed Navy people who are (and should be) worried,” Michael T. Corgan, a Vietnam veteran who teaches international relations at Boston University, said in an email.

“Something of the scope that this scandal embraces didn’t happen without a reasonably widespread acceptance of bad practice,” he wrote.

In exchange for the assistance from the Navy officials, Francis, known in military circles as “Fat Leonard,” lined up prostitutes, hotel stays and tickets to shows, including a Lady Gaga concert in Thailand, according to a criminal complaint.

Francis, who was arrested in September, and his cousin, Alex Wisidagama, a company manager who was also arrested, have pleaded not guilty to charges in the case. Navy Cmdr. Jose Luis Sanchez and Cmdr. Michael Vannak Khem Misiewicz also have pleaded not guilty.

GDMA has provided fuel, food and supplies for Navy ships for 25 years. The investigation started in 2009.

According to the complaint, Beliveau, 44, kept Francis abreast of the Navy’s investigation and advised him on how to respond. He downloaded at least 125 sensitive records from the case files of his fellow Naval Criminal Investigative Service agents, according to charging documents.

The two exchanged thousands of text messages, and at one point, Francis bragged to an associate in an email: “‘I have inside Intel from NCIS and read all the reports,’” according to court documents.