Police in Venice are hoping that a post-mortem examination today on the body of Richard Raynor, the Briton found dead in Venice yesterday, will throw light on whether he committed suicide, was pushed or simply lost his balance while walking late at night along the bridge over the lagoon.

The fully dressed body of Mr Raynor, 23, who went missing while on a Valentine Day break with his girlfriend, was found in shallow water beneath a railway bridge that runs alongside the causeway linking Venice to Mestre on the mainland, where he had been staying with his girlfriend Katie Robinson, 22.

Police said that the body was covered in mud and had "contusions and bruises". The post-mortem examination, to be held at 1pm today at the Umberto I hospital in Mestre, will establish whether the injuries were consistent with an assault or a fall.

Investigators said that it was possible they were sustained when Mr Raynor struck the pillars of the bridge as he fell some 8m (26ft) into the lagoon.

His body was found a kilometre along the 4km (2.5 mile) causeway from Venice in the direction of Mestre, suggesting that Mr Raynor may have tried to walk back to his hotel. This would not explain why his mobile phone, wallet and hotel key were found on the parapet a 100m from where the body was lying. Police are today examining his phone and credit cards for possible clues.

Alessandro Giuliano, head of the Venice flying squad, said that the "working hypothesis" was that Mr Raynor had either committed suicide or suffered an accidental death. Lucia D'Alessandro, the investigating magistrate, said that she was keeping "an open mind, excluding nothing."

Vittorio Borraccetti, the chief prosecutor in Venice, said: "We are taking statements from a number of people and waiting for the results of the post mortem". He said it was not yet clear whether the Venice police would want to question Ms Robinson. "If we need to interview her, we will do so with the help of the British police." he said.

Police said that they had traced the person who found Mr Raynor's personal effects on the bridge parapet and took them to the hotel in Mestre where the couple had stayed, which he was able to identify from the room key. Officers said that the pensioner cycled every day across the causeway, and had handed in the belongings to the hotel after seeing them during his morning ride. The body beneath the bridge was spotted by a passing motor boat.

Mr Raynor's body was identified last night by his father, William, a marine consultant who, had flown to Venice on Saturday to join the search for his son.

Richard Raynor, a computer software engineer, and Ms Robinson, from Retford, Nottinghamshire, had booked a three-day break at the three-star Ariston hotel at Mestre to celebrate the first anniversary of their relationship, flying to Venice last Wednesday from East Midlands airport.

After a "romantic dinner" in Venice that evening, during which they drank "a couple of bottles of wine", they disagreed over whether to return immediately to Mestre by late-night bus, and Ms Robinson said that she went to look for a taxi.

By the time she returned with it, Mr Raynor had disappeared. Believing he had gone for a nightcap, she took the taxi to Mestre on her own. Ms Robinson has said that Mr Raynor phoned her to ask where she was, and told her he would follow in another taxi. She denies that they had a lovers' row or tiff.

The next morning, Valentine's Day, she switched on her mobile phone to find a message from Mr Raynor timed at 1am in which he said that he was "lost in nowhere".

She returned across the causeway by bus to try to find him, but found no trace. She called his mobile phone repeatedly, but there was no reply until 11.30am, when it was answered by the porter at the Ariston Hotel. He told her that Mr Raynor's mobile phone, passport, credit cards, wallet and room key had been handed in.

She reported Mr Raynor's disappearance to police on Thursday afternoon and took the return flight to East Midlands airport from Venice on Friday evening, thinking her boyfriend might show up for the flight. Mr Raynor's mother said her son, who was more than 6ft tall, was "sensible and quiet". His father said he had been a "level headed, steady bloke" who avoided trouble.

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