A slaughtered calf found skinned in a farmer's field may have been a "professional job" for trade.
The animal's skin, head and bones were discovered at Bernwood Meadows in Menmarsh Road, Stanton St John, Oxfordshire.
The incident is thought to have taken place between 1800 BST on Thursday, 26 June, and 0900 BST the following day.
Officers, who have "drawn a blank", want to speak to people who may have seen anything suspicious at the time.
A Thames Valley Police spokeswoman said: "This is quite an unusual, isolated case. We have had a number of similar incidents in other areas such as Buckinghamshire over the past few years but not in Oxford."
PC Andrew Clarke said: "This was a professional job carried out for trade. Our inquiries have not led us to the offender, and we need the public's help to try and resolve the case."