A 41-year-old man has been arrested on suspicion of murder after a body was found in a flat.
Dean Sawyer was found dead on 26 November and police believe his body had been in his home in City Road, Bristol for up to two weeks.
An Avon and Somerset Police spokesman said the 43-year-old had been seriously assaulted.
The arrest follows a search of two commercial premises on West Street on Friday, he said.
Mr Sawyer founded the Positive Causes project based in Old Market, which works with homeless people.
He spoke to BBC Bristol in 2014 about how he used his experience as a former drug user to help people with addictions.
The organisation offers support and counselling, and employs people who struggle find work to distribute a monthly magazine.