Missing Tolworth pensioner John Harding, 82, drowned, a postmortem examination has found.
His body was found in the Thames by Canbury Gardens last Wednesday.
How Mr Harding drowned is to be confirmed at an inquest.
Mr Harding went missing at about 7pm on April 26.
Police glimpsed him a number of times on CCTV but were unable to pinpoint his movements after he was spotted heading towards the Tolworth roundabout on the day he disappeared.