A man posed as a police officer to dupe an elderly victim into handing over her life savings in a courier scam, Scotland Yard said.
The suspect called two south London pensioners pretending to be a police officer investigating a fraud at their bank and asked them to help assist the investigation by withdrawing significant sums of money, the Metropolitan Police said.
He is said to have phoned a 73-year-old woman in Dulwich and instructed her to buy 5,000 euro and a £25,000 watch before a courier collected the items from her house on March 27.
Three weeks later he persuaded an 85-year-old woman in Clapham, to withdraw £5,000 from the bank and asked her to appear at a court hearing as a witness as part of his investigation, Scotland Yard said.
On her return from the bank, the victim is said to have spoken to a neighbour who became suspicious and advised her not to hand over the money to the courier, who left empty-handed.
Police have issued a photo of a man they want to speak to in connection with the scams.
He is described as Asian, about 5ft 8in and in his 20s.
Detective Constable Michael Esangbedo said: "We are now investigating two offences - one, a courier fraud where the deception resulted in the victim handing over her life savings and the other, an attempted fraud which was only prevented due to the vigilance of a neighbour.
"Both were carried out in a similar fashion against elderly, vulnerable victims.
"We would urge anyone who recognises the man pictured to get in touch with police."
Anyone with information should contact Southwark CID on 101 or @MetCC.