Thousands of pounds worth of antiques including furniture and collectables were stolen from a sales room in Norfolk on Friday evening.
Thieves raided the Horners Auction House in Acle where a specialist sale had been scheduled to take place on Saturday morning.
The burglars had disabled security alarms to steal about 300 lots.
As a result of reviewing CCTV footage, officers are keen to trace a white 7.5 tonne van with a black tail lift.
It was seen entering the driveway to the premises at 0430 BST, closely followed by a 4x4 vehicle.
The raid was discovered when staff arrived just before 0700 BST on Saturday.
Some of the items to be sold were from Felthorpe Hall, Norfolk, the home of Geoffrey Watling.
The former President of Norwich City Football Club died last year aged 91.
The antiques include a 19th Century Italian walnut and bone arm chair valued at £1,500, a Tyrolese violin circa 1780 worth £2,000, and an Adolf Schuster violin bow worth £800.
Detectives said they are pursing several lines of inquiry and forensic tests have been carried out at the scene.
Investigating officer Acting Det Sgt Chris Burgess said: "The burglary appears to have been a well planned operation
"We are appealing to anyone who witnessed suspicious activity around the premises at the relevant times."