The body of 44-year-old Maurice Nascimento was found with multiple injuries on Rush Common in July 2021.
Kingston Crown Court was told the chances of it coming from anyone else were a billion to one.
New highly sensitive tests then found similar matches on the dead man’s right hand for co-defendant Ernestas Aleksandrovas.
Police then used CCTV and mobile phone signals to trace the journey of the two 29-year-olds from their home on Norwood High Street to the scene of the murder.
Both will be sentenced at a later date.