He said Clint Rickards' lawyer John Haigh, QC, had obtained the statement during disclosure and shown it to him where he identified a number of errors and became angry with the officer.
Mr McDowell then decided to give defence evidence for Mr Rickards at a trial this year where he was acquitted of alleged sexual offending against a Rotorua woman. Mr McDowell said he believed the officer had changed his statement because it was supportive of Mr Rickards and that didn't fit with the inquiry.
He said he believed the officer wanted to make Mr Rickards look bad "by making me look bad".
"I'm not a lawyer or anything but this sort of stuff needs to be challenged. Our police force needs to be squeaky clean," Mr McDowell said.