An Alaska-based military police officer has been sentenced to 16 years in prison and will receive a dishonourable discharge for selling military secrets to an undercover FBI agent posing as a Russian spy, a military panel has decided.

A panel of eight military members from Joint Base Elmendorf-Richardson in Anchorage recommended a 19-year sentence for Spec William Colton Millay, which was dropped to 16 years because of a pretrial agreement. The panel also reduced him in rank to private.

Millay, 24, pleaded guilty last month to attempted espionage and other counts. A sentencing panel of male military members heard testimony on Monday.

Military prosecutors said Millay was a white supremacist who was fed up with the army and the US, and was willing to sell secrets to an enemy agent even if that would cost his fellow soldiers their lives. Defence attorneys said Millay was an emotionally stunted attention-seeker and was a candidate for rehabilitation.

Millay's attorney, Seattle-based Charles Swift, said he understood and accepted the sentence.

However, he said: "We do intend to seek further clemency as this case goes forward for the reasons that were set forth in the trial: his mental state, his emotional age, and the motivation for it, and the circumstances."

Monday's proceedings were like a mini-trial conducted in front of the sentencing panel, with each side calling two witnesses.

Special Agent Derrick Chriswell said Millay came to the FBI's attention in the summer of 2011 through an anonymous tipoff after Millay sent an email to a Russian publication seeking information about the military and made several calls to the Russian embassy.

"That's a concern for national security," Chriswell said.

The FBI, working with military intelligence agencies, conducted the investigation. On 13 September 2011, an FBI undercover agent called Millay and set up a meeting the next day at an Anchorage hotel restaurant.

Chriswell testified that during the first meeting with the agent that day, Millay "expressed his disgust with the US military". They then moved to the agent's hotel room, where audio and video recording devices were in place.

Millay said he would work for the Russian government, and if they made it worth his while he would re-enlist for a second five-year stint. He also said he had confidential information on the Warlock Duke jamming system the US military uses to sweep roadside bombs.

Two days after that meeting, Millay reported to his commander that he had been contacted by a Russian agent. He was later interrogated by military intelligence officers and the FBI, but prosecutors say Millay was merely trying to throw off suspicion.

Chriswell said Millay withheld information during the interrogation that officials already knew from the recordings. That included a claim that he did not know why a Russian agent would contact him, his claim to the agent that he had access to social security numbers of people on base because of his police job and that he had sent an earlier text claiming he had more information on the jamming system.

Later, after Millay came off a month-long leave, he told the agent he was willing to sell information using a confidential drop at a park.

On 21 October 2011, he dropped off a white envelope with information about the F-22s and the jamming system in a rubbish bin. That envelope was later collected by the FBI.

Millay was told to drive to a hotel, where he collected $3,000 (£2,000) and a disposable cell phone from a pickup.

The agent contacted Millay afterwards to complain her superiors wanted information that was not on the internet. Millay assured her that the information on the jamming system – about a paragraph's worth – was not available. That was later confirmed by military personnel.

He was arrested on 28 October. A search of his barracks found two handguns, detailed instructions on how to use a Russian internet phone service and literature from the white supremacist organisation the National Socialists Movement.

Chriswell also testified that Millay had two Nazi SS thunderbolt tattoos under his biceps and spider web tattoos, which he said were common among racists in prison.

"He branded himself in their symbols of hate," the military prosecutor Captain Stewart Hyderkhan said in his closing statement, arguing for a sentence of at least 25 years in prison. "He had hate for the army. He had hate for the United States."

Swift, Millay's attorney, argued that the Nazi movement and Russia did not have much in common, and that Millay had once been married to a Filipina.

The defence witness Dr Veronica Harris, a psychiatrist, testified that Millay had the emotional capability of a five-year-old and suffered from low self-esteem, mild depression, alcoholism and narcissism.

Millay offered an unsworn statement to the court, in which he said: "This has destroyed me."

"I know I've made a terrible mistake," he said, fighting back tears. "I'm a US soldier, and that piece of me I'm proud of."

Millay spoke of his demon within. "It has taken me three years to come to grips with who he is," he said. "He's my worst enemy; my worst enemy is myself."

Hyderkhan said that was not remorse, especially since prison recordings showed he threatened to continue to divulge secrets.

Swift, in his closing statement, argued that eight years was punitive enough and would provide time for rehabilitation.