The police watchdog is investigating claims that an officer from Greater Manchester failed to disclose evidence at a fraud trial.
Last week the Court of Appeal quashed a man's conviction from 2001 after it was deemed unsafe.
The man was jailed for two counts of obtaining services by deception.
The Independent Police Complaints Commission (IPCC) is investigating claims that an officer submitted a misleading statement at his trial.
It is also alleged that the Greater Manchester Police officer failed to disclose information relating to the credibility of a key prosecution witness.
The man was sentenced to nine months' imprisonment.
Naseem Malik, IPCC Commissioner for the North West, said: "This is a serious matter in which it is alleged a police officer failed to disclose evidence in a criminal court case.
"That court case led to the conviction of a man and we now know that conviction to have been unsafe. It is important the matter is investigated thoroughly and independently to determine how and why this failure occurred."