Detectives investigating the Hatton Garden raid are still hunting a mystery key suspect amid fears he could have fled abroad.
The Metropolitan Police's Flying Squad issued an urgent public appeal for help in tracing the thief, known only as "Basil", and the missing two thirds of the £14m loot.
It comes after three men were found guilty of being involved in the raid, which took place over the Easter weekend last year and is believed to be the biggest burglary in British history.
Carl Wood, 58, and William Lincoln, 60, were convicted of conspiracy to commit burglary and conspiracy to conceal, convert or transfer criminal property, while plumber Hugh Doyle, 48, was found guilty of concealing, converting or transferring criminal property between January 1 and May 19 last year.
They were members of the gang, including five others, who ransacked 73 boxes at Hatton Garden Safety Deposit after using a drill to bore a hole into the vault wall.
Valuables worth up to £14 million, including gold, diamonds and sapphires, were taken, but only a third have been recovered.
Officers have so far been unable to identify Basil, prompting fears he could have left the UK unchecked.
The key player let his co-conspirators into the building by opening the fire escape from inside, is thought to have disabled the alarm and also climbed through the hole in the vault wall, along with another man, to get at the deposit boxes.
Head of the Flying Squad Detective Superintendent Craig Turner said: "One man who has become known as 'Basil' is still wanted in connection with the burglary.
"We would ask anyone who has information as to the identity of 'Basil' or the whereabouts of the outstanding jewellery to contact police.
"We are offering a reward of up to £20,000 for information leading to his arrest and conviction and the recovery of the outstanding property."
The Daily Mirror quoted an "underworld source" as saying: "He's a clever kid and the police won't have much on him, he's too good for that. He will have hidden his whack somewhere secure in the UK and gone on his toes."
The paper said Basil, reportedly nicknamed "The Ghost", is from the South East, is around 6ft, slightly built and in his mid-50s. He is believed to have worn a ginger wig over greying brown hair during the raid, it adds.
As well as the three convictions yesterday, ringleaders John "Kenny" Collins, 75, Daniel Jones, 60, Terry Perkins, 67, and the group's oldest member Brian Reader, 76, pleaded guilty to conspiracy to commit burglary last September.
Collins, of Bletsoe Walk, Islington; Jones, of Park Avenue, Enfield; Perkins, of Heene Road, Enfield, and Reader, of Dartford Road, Dartford, have been in custody since their arrests.
They are due to be sentenced along with Wood, of Elderbeck Close, Cheshunt, Hertfordshire, Lincoln, of Winkley Street, Bethnal Green, east London, and Doyle, of Riverside Gardens, Enfield, north London, by Judge Christopher Kinch QC on March 7.