Stephen Pollard, who was 58, was reported missing on February, 27, 2015, and his body was found on the banks of the River Aire, between Beal and Birkin in North Yorkshire, on May 22 that year.
His death was not treated as suspicious at the time but new information led detectives to re-investigate.
A 51-year-old woman from the York area has been arrested on suspicion of assisting an offender.
This comes after two men from the York area, aged 24 and 52, and a man from the Wakefield area, aged 52, were arrested on suspicion of murder this week.
All three men have been released pending further enquiries.