Police say he was spotted walking up Whyteleafe Hill in Whyteleafe at around 6.15am on March 30.
Later that morning the body of 48-year-old Mario Commatteo was discovered at home with a shot-gun blast to his head.
Police said the crime bore the signs of a contract killing.
Detective Chief Inspector Adrian Leppard said he would like to trace the man witnesses had seen and was interested in hearing from anyone who may know his identity.
He is described as white, in his 20s and of average height with cropped blond hair. He was wearing a blue and white waterproof-type jacket, jeans or tracksuit trousers and carrying a drawstring bag under his left shoulder.
"It's important to identify and eliminate him at the earliest opportunity," said Det Chief Insp Leppard.
If you have any information call Horley Incident Room on 01737 765 040.
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