John Beliveau Jr., center, and his attorneys, Gretchen von Helms, left, and Jessica Carmichael, arrive at the federal courthouse in San Diego on Dec. 17, 2013. (Lenny Ignelzi/AP)

A federal judge sentenced a former Naval Criminal Investigative Service agent to 12 years in prison Friday for leaking confidential law-enforcement files to an Asian defense contractor who seduced him with cash bribes, booze and prostitutes.

John Beliveau, Jr., a one-time NCIS agent of the year, received the most severe punishment imposed so far in a corruption scandal that has ensnared 16 other criminal defendants and rocked the Navy.

Beliveau, 47, who pleaded guilty shortly after the scandal became public in 2013, has admitted to leaking hundreds of sensitive NCIS files to Leonard Glenn Francis, a Singapore-based contractor who supplied Navy ships throughout Asia. Francis, a rotund and charismatic man known as “Fat Leonard,” exploited the leaked information to thwart NCIS investigations into his company for years.

Beliveau’s attorneys said he betrayed his country because he had a fragile psyche and became “clinically obsessed” with a crooked Asian defense contractor who easily reeled him in with bribes. They asked that he be spared any prison time, while prosecutors had sought a 15-year sentence. The punishment was handed down late Friday by U.S. District Court Judge Janis Sammartino in San Diego.

NCIS officials have described Beliveau as one of the worst traitors in the agency’s history. He met Francis after he was assigned to Singapore as a counterterrorism agent in 2008 and quickly fell under the defense contractor’s spell, according to his attorneys.

Francis was a legendary figure in Navy circles who treated officers to lavish meals and parties — featuring Cuban cigars, expensive champagne and strippers — when their ships made visits to Asian ports. In court papers, Beliveau’s lawyers described him as particularly susceptible to Francis’s charms because of his fondness for alcohol, a history of mental illness and a lifelong lack of sexual experience with women other than prostitutes.

According to his lawyers, Beliveau had struggled with obsessive-compulsive disorder since he was a child and was debilitated from cancer treatments when he arrived in Singapore. Soon, he contracted dengue fever during a visit to the country of East Timor and also developed post-traumatic stress disorder after a bizarre incident during which he witnessed, up close, the beheading of a gang member.

Given his physical and emotional weaknesses, Beliveau became a “prime target” for Francis, who supplied him with sex workers, $30,000 in cash and travel, alcohol and a “perceived friendship,” the agent’s attorneys said in court papers. Eventually, they added, Beliveau became “symptomatically obsessed with Francis, and overwhelmingly attached to the relief Francis could provide through the parties and prostitutes.”

“I have betrayed the badge I wore, the oath I took, my comrades,” Beliveau said in a letter to the judge. “I deserve and understand the feelings of anger, vengeance and disgust from others in my former field.”

In asking for a 15-year prison term, prosecutors noted that Beliveau “caused incalculable injury” to the reputation of NCIS and its long-standing efforts to prove that Francis was fleecing the Navy for supplies, fuel and port services. In handing over so many confidential files over a two-year period, they said, Beliveau tipped off Francis to the identities of several cooperating witnesses, including some who had agreed to wear wires for NCIS, and also advised the contractor on how to erase incriminating evidence.

Prosecutors also said Beliveau was under no illusions about the nature of his transactional relationship with Francis, regularly demanding money and prostitutes in exchange for leaked material.

“I will always be your friend, but you will get nothing else … until I get what you promise,” he said in an email to Francis in April 2012. “You give whores more money than you give me. … I can be your best friend or your worst enemy. I am not an amateur.”

Francis has also pleaded guilty to bribery charges and has admitted that his firm overcharged the Navy by at least $35 million. He has been in federal custody since he was arrested in a sting operation in San Diego in September 2013. His sentencing is scheduled for next summer.

Eleven current or former Navy officials — including a one-star admiral — have been charged in the case. Many other Navy officers remain under investigation.