(CNN) -- Insurers Lloyd's of London is offering a reward of up to €1 million ($1.3 million) for information that will lead to the recovery of the jewels stolen from an exhibition in the French resort city of Cannes last month.
"A reward of up to €1 000 000 pro rata is offered to the first person who provides information which leads to recovery of the goods. Offer subject to certain conditions," the insurer said in a statement Tuesday.
The robbery took place July 28 at a jewelry exhibition in the luxury Carlton Hotel -- the third gem theft around the city since May.
The Nice prosecutor's office told CNN on Monday that the value of the stolen jewels was close to $136 million.
The robber, whose face was covered by a hat and a scarf, had a semiautomatic pistol and threatened to shoot the exhibitors and guests, according to Philippe Vique, deputy prosecutor for organized crime in the prosecutor's office.
Security guards were present but unarmed, he said. No one was injured.
"It was definitely a professional heist, I've been saying that from day one," said Larry Lawton, who himself served time for jewelry thefts but is now an author and motivational speaker.
He suspects the Cannes thief had an "inside guy" who provided information on where to find the jewels.
The robbery follows two major jewel heists this year during the Cannes Film Festival in May.
A necklace worth $2.6 million was stolen from a hotel party shortly after jewels worth more than $1 million were stolen from a safe in a hotel room.