A 91-year-old woman had cash stolen from her after a man asked her if she could change a £2 coin.
The incident happened in Station Road, Desborough, between 10.15am and 10.30am on Wednesday, May 24.
A police spokesman said: “The victim was approached by a smartly dressed man and was looking in her purse for change for him, struggling to remove the coins.
“He then reached in, pretending to help, and is believed to stolen £70 from her purse.
“This was her pension.”
The offender is described as white, aged between 30 and 40-years-old with a medium build, between 5ft 7in and 5ft 9in, with dark, medium-length hair and a local accent.
He wore a black suit.
Anyone with information can contact Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.