Three men have been arrested in connection with the inquiry.
Two of the men aged 25 and 20 have been arrested on suspicion of murder, while a 29-year-old man has been arrested on suspicion of assisting an offender.
All three are from the Ravensthorpe area.
The 37-year-old’s death was initially treated as unexplained when he was found in a wooded area close to the canal running through Ravensthorpe.
Police were keen to speak to anyone who could provide information about Mr Siarczylski’s general lifestyle or movements prior to his death.
As a result of the appeal, new information came to light which led to the murder investigation being launched.
Det Ch Insp Mark Swift, of the Homicide and Major Enquiries Team, said: “We would like to thank the public for their response to our appeal last week for information about Mr Siarczylski’s lifestyle or his movements prior to his death.
“As a result new information has come to light which suggests that Mr Siarczylski may have been murdered.
“Three men have been arrested in connection with this inquiry and remain in custody.”
The body was found in a wooded area off Low Mill Lane, close to the Calder and Hebble Navigation Canal.
Anyone with information should contact the Homicide and Major Enquiry Team via 101.
Information can also be given anonymously to Crimestoppers on 0800 555 111.