Officers investigating the killing of a notorious gangster are looking at potential links with five other deaths.

John “Goldfinger” Palmer was shot six times in the grounds of his cottage after being watched through a spyhole in his fence, it was recently revealed.

Police have said the murder had “all the hallmarks” of a professional hit.

A £50,000 reward was doubled to coincide with the anniversary of his death in June this year.

The campaign for information has prompted a “number of calls” to Essex Police which has confirmed they are investigating some new leads.

An Essex Police spokesman said: “Mr Palmer’s family, with the support of Crimestoppers, offered a reward of up to £100,000 for information leading to arrest and conviction of the person or people responsible for Mr Palmer’s murder. Since our appeal, we have received a number of calls with information which have instigated further lines of inquiry.”

Now detectives are investigating whether five other deaths could be connected.

They include the murder of a British couple in 2006 and the death of Palmer’s former henchman three months before the crime boss’s murder, according to the Mirror.

Expats Billy Robinson, a member of Palmer’s gang, and his wife Flo were found dead near their home in Tenerife.

The couple were kidnapped before they were both brutally murdered.

Palmer – who earned his nickname after being cleared of helping to dispose of gold from the £26million Brink’s-Mat robbery at Heathrow Airport in 1983 – had returned to the UK, after being released halfway through an eight-year prison sentence for a £30million fraud.

Three months before Palmer’s death – in Brentwood in June, 2015 – another one of his former gang members, Dennis New was found dead at 58.

The death of timeshare shark Garry Leigh, 47, in 2010, is also being investigated as linked.

He was run over during a Saturday cycle ride in Marbella on the Costa del Sol.

The fifth death being investigated for possible links to the Palmer murder is that of former soldier Dale Moore in February 2005 in Tanzania.

Palmer ran a timeshare racket in Tenerife during the 1980s and Spanish police suspect an Eastern European crime gang looking to move in on the business was behind the murder.