A reward of up to £100,000 has been offered for information on the theft of a diamond tiara from a country estate.
The Portland Tiara, from The Welbeck Estate near Worksop, Nottinghamshire, was taken along with a diamond brooch on 20 November 2018.
A police appeal featured on BBC One's Crimewatch Roadshow Live on Monday.
Six people - five men and one woman - have been arrested and released under investigation, Nottinghamshire Police said.
Speaking after the programme aired, Det Insp Gayle Hart said: "We're still pursuing a number of lines of enquiry but we believe there are people out there who may have crucial information that could help with our investigation."
The force wants to hear from anyone with information on a silver Audi S5 found burnt out in Cross Lane, Blidworth, about 30 minutes after the burglary.
A private appeal offering the reward is being administered by The Art Loss Register.
The arrested men - aged 47, 39, 38, 34 and 24 - and a 31-year-old woman were held on suspicion of conspiracy to burgle and released under investigation.