Police investigating the killing of an Auckland taxi driver have revealed they have found another item of clothing that may belong to the killer.

Hiren Mohini, 39, was stabbed by a passenger in what police describe as a frenzied attack about 1.30am on 31 January after picking up a fare from the city.

Police are still trying to identify a man seen in security camera footage shortly before the pick-up.

NEW EVIDENCE: Police have found a distinctive knitted dark cap with a large white logo outlined with three circles.

On Tuesday, they revealed that a distinctive knitted, dark cap with three circles on it was found beside a blood-stained blue bag near where the killing took place.

The cap is being forensically examined.

Detective Inspector Hywel Jones says police want to know who owned, used or wore the bag and cap.