CCTV footage of three raiders who used specialist diamond cutter tools to steal a famous "national treasure" tiara has been released by police.
The Portland Tiara was stolen from the Welbeck Estate between 9.45pm and 10pm on November 20, Nottinghamshire Police said.
The brazen burglars broke into the Portland Collection Gallery and stole a diamond brooch from an armoured glass display as well as the precious item, which had been seen by countless members of the public.
The footage released by the force features three suspects who are wanted in connection with the incident.
Police said they are also appealing for information about a silver Audi RS5 Quattro, registration number KY61 USJ, which is believed to have been involved in the burglary.
The car was stolen from the Phoenix Park park and ride tram stop on Millennium Way East, Cinderhill, Nottingham, on November 2 and was found abandoned and burnt out in Cross Lane, Blidworth, around 30 minutes after the burglary.
Detective Inspector Gayle Hart said: "Our inquiries are ongoing and we're making a plea to potential witnesses.
"The suspects were wearing white suits and motorcycle helmets but we're still hoping someone may know who they are and we're urging anyone with any information to get in touch with us.
"We're also urging anyone who has any information about the silver Audi RS5 to contact us."
Ms Hart added: "Did you see this car in the area around the time of the burglary or have dashcam footage of it? Did you see anyone in the car?
"We're keen to trace this vehicle's movements preceding the burglary, so again we're appealing to anyone who saw it or who has any information to get in touch with us as soon as possible.
"We believe the burglars used specialist diamond cutter-type tools to break through the armoured glass display case. If anyone has information about people hiring or sourcing such equipment then we'd urge them to get in touch."
In a statement, the Welbeck Estate said it was "deeply saddened about the robbery" and continues to assist police with their inquiries.
The Nottinghamshire force have asked anyone with information to come forward.