A confused pensioner was conned out of more than £11,000 by a man who called repeatedly saying the victim owed him money.
From October last year the conman regularly knocked on the victim's door and said: "Remember me? You owe me money."
The victim each time handed over cash and it was only recently that worried neighbours and relatives discovered what was happening and reported the matter to police.
Detectives estimate the trickster got away with £11,500.
A Brighton and Hove police spokesman said: "The offender deliberately targeted a very elderly victim who was too confused to know what was going on.
"It is despicable and we would urge everyone to be on guard and to watch out for vulnerable neighbours and relatives."
Police said the con was one of several reported recently and they warned all residents not to let strangers into their homes.
Police urged people to dial 999 if they see anyone acting suspiciously or 0845 6070999 if they have information on bogus callers.
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