A detective who was an international expert on fraud has been jailed for two years for his part in a plot to trade a forged bond worth $500m (£270m).
Det Sgt William McKelvie, 44, from Esher in Surrey, was sentenced on Wednesday at Southwark Crown Court.
He used his police contacts to help former colleague Robert Miles, 47, of Towcester, Northants, who was trying to sell the draft.
McKelvie was convicted of three charges of misconduct in a public office.
He was cleared of charges of conspiracy to pervert the course of justice.
McKelvie was head of the West African organised crime section at the National Criminal Intelligence Service (NCIS) when he was contacted by Miles, with whom he worked at Clapham police station in London during the 1980s.
Miles obtained the fraudulent $500m draft in 2003.
It had been created by a known forger in America and was purportedly authorised by the Ford Motor Corporation.
The court heard that suspicions were aroused when Miles tried to present the bond at banks.
He enlisted the help of McKelvie, who kept track of a police probe into the plot, at one stage generating a false intelligence report in order to keep investigators off Miles's trail.
Andrew Wheeler, prosecuting, said McKelvie had established beyond doubt that the draft was bogus and told Miles both in writing and orally.
He also informed Miles and his gang of English associates that an NCIS money laundering probe had begun into them, which, according to Mr Wheeler, "seriously prejudiced" the investigation.
'Abuse of trust'
Miles had left the police force in 1989, moving to Spain where he became a property investor.
His counsel argued that he believed the bond to be genuine and was the victim of a con, a claim which Judge Christopher Elwen branded as "completely implausible".
Miles was found guilty of aiding and abetting misconduct in a public office and given one year in prison.
He was also acquitted by a jury of conspiracy charges.
Sentencing the pair, Judge Elwen told McKelvie: "You must have known what you did was an abuse of trust as a serving police officer.
"Your motivations... were the prospect of financial gain."
Judge Elwen said he had taken into account many commendations received by the detective, but there was still no choice but to impose a two-year custodial term.