Born in 1961 in St. Paul, Minnesota, the grandson of the Chief of the Winnebago Native American tribe.

Enlisted in the United States Marine Corps in 1980 and entered the Marine Corps Security Battalion Guard school, a rigorous, elite training program in which he was instructed in espionage and counterespionage techniques. Was given TOP SECRET security clearance and was assigned to the U.S. Embassy in Moscow in 1984.

As part of his assignment, he signed a non-fraternization agreement, thereby promising not to engage in friendships with Soviet citizens and to report any such contacts. Lonetree apparently received undo attention because most citizens of Moscow had never seen a Native American before. Despite such attention he was described as lonely and somber and was believed to have begun drinking excessively.

Attended the annual Marine ball in November 1985 and was introduced to Violetta Seina, a 25 year old Russian woman who was an embassy employee. The two began dating soon thereafter. Was part of the the Marine unit assigned to provide security for the 1985 summit meeting between Soviet premier Mikhail Gorbachev and U.S. President Ronald Reagan.

Was introduced by Violetta to her “Uncle Sasha”, who in reality was a KGB intelligence officer (named Aleksiy Yefimov). Sasha recruited Lonetree to become a “friend of the Soviet Union.” Lonetree eventually provided Sasha with information about the embassy and the U.S. Ambassador. Sasha also asked him to plant a “bug” in the Embassy but Lonetree allegedly refused to do, but instead provided plans for the building.

Was assigned to the U.S. Embassy in Vienna, Austria in March 1986. While in Vienna, Lonetree met with Sasha and provided him with information about embassy employees and with floor plans to the building. In return he was given $2,500 US. Over time, Lonetree provided TOP SECRET documents as well as a burn bag containing more than 100 documents related to U.S. arms reduction.

On December 12, 1986, Sasha turned Lonetree over to another handler, who promised to aid Lonetree in re-uniting with Violetta. Two days later, however, Lonetree reported his actions to the CIA station chief. He was immediately turned over to the Navy Intelligence Service (NIS) and placed under arrest, charged with espionage.
NIS launched a nine month investigation, during which all of the Marine guards in the Moscow embassy were replaced. NIS also arrested Corporal Arnold Bracy, who signed a confession indicating that he acted as a lookout for Lonetree, while Lonetree secreted KGB operatives into the embassy to plant bugs. Also arrested was Marine staff Sergeant Robert Stufflebeam, who was charged wit failing to report fraternization with Soviet women. The charges against Bracy and Stufflebeam were eventually dropped.

NIS was highly criticized for its over-exuberance with its investigation, accused of blowing things way out of proportion in order to show off having disrupted a spy operation. Lonetree was convicted on multiple counts of turning over classified information, was court-martialed in 1987 and sentenced to 30 years in prison. He was the first U.S. Marine Corps member ever convicted of espionage. Because of his cooperation with authorities, his sentence was reduced to 25 years of which he served nine before being released in February 1996.