Police have found a lorry believed to have been used in the theft of a £3 million Henry Moore sculpture.
They also want a mystery caller with potentially useful information to make contact again.
Officers discovered the Mercedes flat-bed lorry, which is thought to have driven off with the two-tonne Reclining Figure, in Brickfield Lane, Coopersale, near Epping, Essex.
The lorry with a lifting crane on the back, had been stolen from an address in Roydon, Essex, around an hour before the theft.
The massive bronze sculpture, was lifted on to the back of the truck by a gang and stolen from the Henry Moore Foundation in Perry Green, Much Hadham, Hertfordshire, at around 10.10pm on Thursday evening.
The work of art, which measures three metres long and two metres high (10ft by 6.5ft), was spotted by a member of the public on the back of a lorry within an hour of the theft, police said.
The lorry was seen 12 miles away in Harlow, Essex.
Detective Sergeant Graeme Smith said: "A member of the public has reported seeing the lorry with the sculpture on the back at 10.45pm on Thursday night.
"The lorry was seen in Southern Way at the junction with Parkington Road, Harlow.
"We are appealing for members of the public who live in or travel through these areas, to contact police if they
saw this vehicle, or if they saw any suspicious activity in the area around that time."
Police fear thieves may have stolen the 1969/1970 work to melt down and sell for scrap. Despite its multi-million pound value, the metal would only fetch an estimated £5,000 on the open market.
The Henry Moore Foundation is offering a "substantial" reward, in excess of the £5,000 that would be gained from selling the scrap metal, for information leading to its recovery.
In a separate line of inquiry, police are appealing for a member of the public who called Crimestoppers last night with potentially crucial information to call back.
A spokesman said: "Crimestoppers received a call last night with some information which may be vital to our investigation. We are appealing for this person to re-contact Crimestoppers or police, so that we may discuss their information more fully.
"We will deal with any calls in the strictest of confidence and you do not have to give your name or details to police.
"Our major concern at this time is the safe recovery of the sculpture. This is a national treasure and the foundation is offering a far more substantial reward than any value the thieves might gather from disposing of the bronze as scrap metal."
The statue was taken from a farmyard next to the visitor centre. It had been there for only a couple of days awaiting repositioning after being removed from the field.
Police believe the thieves knew what they were after when they struck.
The theft was captured on CCTV and footage shows three men entering the courtyard in two vehicles.
Police are still searching for the second vehicle, believed to be a Daihatsu four-wheel drive with spotlights on the front.
One of the three suspects wore a hooded jacket and another wore a baseball cap.
Anyone with information should contact police on 0845 3300 222 or 01992 533 002, or Crimestoppers on 0800 555 111.