Picture of Amelie witness

This is the man police believe holds the key to finding the killer of French student Amelie Delagrange.

Minutes after the scene was taped Miss Delagrange, 22, was battered to death with a blunt instrument on Twickenham Green.

The CCTV footage taken along Hampton Road shortly before 10pm on 19 August reveals a man a few yards in front of Miss Delagrange.

Officers do not believe she was followed and the man could have seen her killer near the green or waiting in a vehicle nearby.

Miss Delagrange was walking towards her home from Fulwell bus garage after taking the wrong bus. She had left Cristalz bar in Twickenham and boarded a 267 bus service which took her to the bus garage. Six minutes later CCTV caught her walking past the Loch Fyne Restaurant and then a busmounted camera - intended to film motorists using the bus lane - caught her walking towards the green at 9.59pm.

Police released the footage in an effort to jog people's memories and encourage the witness to come forward.

He is described as white with dark hair and was wearing a white T-shirt and blue jeans with a dark jumper over his shoulders. DCS Andy Murphy, head of the Specialist Crime Directorate West, leading the investigation, described the man as a "very significant witness".

"This footage was taken a hundred yards before Am鬩e reached the green and minutes before her death. Despite our best efforts we have not yet managed to trace the man in these pictures who we believe could be a very significant witness," he said.

"This man may not be aware that Am鬩e was behind him or he may think that he saw nothing that can assist us with our enquiries.

"We would like him or anyone who knows him to contact us. He could have walked past Am鬩e's killer or seen him waiting in a car near the green."

Following a reconstruction of her last movements, police received more than 100 phone calls from the public. Miss Delagrange's brown leather bag and Sony mobile phone, which were taken during the attack, have not yet been recovered.

Her purse, keys and Walkman were found dumped in the river at Walton-on-Thames.

A man arrested and quizzed over the weekend is being detained under the Mental Health Act. Police are seeking to establish whether there is a link with similar attacks including the murder of 19-year-old Marsha McDonnell last February less than three miles away.