He was Richard Copithorn, 41, who lived alone in King Edward Avenue, Worthing.
Detective Chief Inspector Pierre Serra said: “We are investigating the circumstances on behalf of the Coroner. His death was unexpected but is not being treated as suspicious.
“We would appeal to anyone who witnessed the incident to call police on 101 to help us understand exactly what happened.
“Sussex Police, along with two other agencies, had been working together to support Richard Copithorn.
“Our sympathies go to Richard’s family following his death. We also pledge our full assistance to the IPCC review into previous police interaction with Mr Copithorn.”
An investigation has also been opened into prior police contact with Mr Copithorn, most recently the police response to a telephone call to the police contact centre the day before his death.
Police are also liaising with local partners regarding multi-agency interaction with Mr Copithorn over the last two years, to see if there are lessons to be learned in how we responded to and supported Mr Copithorn.