Officers investigating the death of a 21-year-old who drowned in the Thames on June 19 passed the case up to the serious crime directorate last week.
The death of Surbiton resident James Spencer is still not being treated as suspicious, but investigations will be carried out more effectively with greater resources.
Mr Spencer was drinking on a boat with his friends on the night of his death and got into difficulties after entering the water at about 12.30am.
Police believe there was an altercation earlier in the night and are keen for witnesses to come forward.
A police spokesman said: "It is still being investigated and is still being treated as unexplained.
"There is nothing suspicious from the postmortem examination so it’s just about making sure nothing has been missed really."
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