(CNN) -- A twice-convicted former CIA officer has been sentenced to an extra eight years in prison for spying for Russia.
Harold James Nicholson, 59, received the sentence for continuing his covert activities while incarcerated, the U.S. Attorney's office said in a statement Tuesday afternoon following the court hearing in Portland.
Nicholson admitted to working through his son to secretly pass information to and get payments from Russia.
The elder Nicholson received a 23-year sentence in 1997 after pleading guilty to spying for Russia, one year after he was arrested at Dulles International Airport outside Washington while attempting to board a flight to Switzerland. The new sentence will be served after the original one.
Federal prosecutors said that at the time of his arrest, Nicholson was carrying 10 rolls of film of classified documents as well as coded messages on a computer disk. They said he planned to meet his Russian handlers, who would pay him more than $180,000.
But his covert, and profitable, relationship with the Russians did not end while he was imprisoned at the Federal Correctional Institution in Sheridan, Oregon.
Nicholson admitted as much in November, when -- 21 months after being indicted again -- he pleaded guilty to conspiracy to act as an agent of a foreign government and conspiracy to commit international money laundering as part of an agreement with federal prosecutors.
At that hearing, the 16-year former CIA station chief confessed to working with his son, Nathan, to funnel information to and get money from the Russian government between 2006 and December 2008. Meetings took place in San Francisco; Mexico City, Lima, Peru; and Nicosia, Cyprus; among other locations.
Nicholson could have faced 25 years in prison and $750,000 in fines for both crimes. But instead, he had eight years tacked onto his existing sentence per the plea deal, a statement from the U.S. Attorney's office in Oregon said.
"Today, former CIA official Harold Nicholson is being held accountable for once again violating his oath to protect America's national security," said David Kris, assistant attorney general for national security, in a statement released Tuesday.
According to court documents, Nathan Nicholson, 26, cooperated with prosecutors in their case against his father after FBI agents confronted him about frequent international travel.
Nathan Nicholson told the agents that at his father's behest, he met with Russian government representatives who gave him payments totaling more than $35,000 in cash.
During Nathan Nicholson's prison visits to his father, according to court records, "Harold Nicholson spent a significant amount of time advising (the) defendant on how to conduct himself in a clandestine manner as he traveled to and from various international meeting locations. Harold Nicholson tried to impart his CIA training to (the) defendant."
Prosecutors alleged the Russians gave the elder Nicholson back-pay for his prior espionage activities and for details on how he was caught.
According to court records, the elder Nicholson and his son put the plot into motion after Nathan Nicholson complained to his father about the family's precarious finances.
The sentencing memo said that Nathan Nicholson provided crucial help in the prosecution of his father. The elder Nicholson pleaded guilty on the day that his trial was set to have begun last month.
"Harold Nicholson betrayed his country and he betrayed his family -- and stooped so low as to involve his son in his corrupt scheme to collect money for his spying," said U.S. Attorney Dwight C. Holton.
According to Holton's office, this case is the first time a convicted spy has been convicted of new crimes involving a foreign country he or she spied for, while serving a sentence for espionage.
CNN's Patrick Oppman contributed to this report.