CCTV footage of three assailants who used special diamond cutting tools to steal a famous National Treasure tiara was released by the police.
The Portland Tiara was stolen from the Welbeck Estate on November 20 between 9:45 and 10:00 pm, police from Nottinghamshire said.
The iron burglars broke into the Portland Collection Gallery and stole a diamond brooch from a bulletproof glass display and the precious object that countless visitors had seen.
The material published by the troupe shows three suspects who are being sought in connection with the incident.
The police said they were also asking for information on a silver Audi RS5 Quattro with registration number KY61 USJ, which was probably involved in the break-in.
The car was stolen from the park in Phoenix Park on November 2 and stopped at the Millennium Way East tram stop (Cinderhill, Nottingham). It was found abandoned and burned about 30 minutes after the break-in at Cross Lane, Blidworth.
Detective Inspector Gayle Hart said, "Our investigations are ongoing and we are calling for potential witnesses.
"The suspects wore white suits and motorcycle helmets, but we still hope someone knows who they are, and we urge anyone with information to contact us.
"We also call on all who have information about the silver Audi RS5 to contact us."
Ms. Hart added, "Did you see this car around the time of the break-in or do you have a Dashcam video of it? Did you see someone in the car?
"We want to track down the vehicle's movements before the break-in, and we appeal to anyone who has seen it or who has the information to contact us as soon as possible.
"We believe that the burglars used special tools with diamond cutters to break through the bulletproof glass cabinet. If someone has information about people renting or procuring such equipment, we urge them to contact you. "
In a statement, Gutshof Welbeck said he was "deeply saddened by the robbery" and continued to assist the police in their investigation.
The Nottinghamshire troupe has asked everyone to share information.