A recycling wheelie bin missing from Carmen Thomas' home could be one of a number of vital links in the search for her body.

"The serial number on the Auckland City Council blue-lidded 240 litre bin is 014 172 and if anyone knows where it is, they should contact us," says the head of the homicide investigation, Detective Inspector Mark Benefield.

"We don't know when it went missing and we won't know until we find it whether it's of significance to our investigation, but we'd very much like to locate it so that we can make our own determinations as to its importance or otherwise."

Mr Benefield said it was distressing for the investigation team to have to report to Carmen's family that Police believe she's been killed, but staff are firmly committed to finding her and bringing whoever is responsible for her death and disposal to account.

He said while a lot of information had been collated, there were still many areas where help from the public would greatly boost progress of the investigation.

"Who drove Carmen's car to Hamilton? Our significant inquiries around dates and times of movements of her vehicle lead us to believe it arrived in Hamilton on the night of July 7 and was left abandoned in Dyer St.

"If anyone recalls seeing it being driven any time between June 28 and July 8 and can provide us with information about who was in it, they should contact us.

"In addition to blood in her car there is other forensic evidence we're aware of that I'm not at liberty to elaborate on now but, suffice to say, we are convinced that Carmen was killed and we want to know who did it and when.

"More than two weeks ago we acknowledged that the investigation into her disappearance was looking increasingly sinister. In light of everything I now know, I can confirm that we are investigating a homicide rather than a missing person situation."

In summary, Operation Keppel needs information about:

•Where Carmen is
•Who drove Carmen's car to Hamilton late on July 7?
•Where is the wheelie bin - serial number 014 172
•Any items that belonged to Carmen that are missing from her home or car -
ie turquoise handbag, car keys for her dark Nissan Pulsar 3-door hatchback registration number ATS 209, identification documents (eg driver's license, wallet, credit cards)
•Anyone who has been behaving unusually at the mention of Carmen's name
since about June 27 or at mention of the Police investigation into her disappearance since she was reported missing on July 13.