Detectives hunting a man of interest in the Sabina Nessa murder inquiry believe that a “reflective red item” the suspect was seen carrying on the night of her death may have been used in the attack.

CCTV footage of the figure shows him looking over his shoulder, putting up his hood and attempting to conceal the red item on the night of Nessa’s death in Kidbrooke, south-east London.

Detective chief inspector Neil John, from the Metropolitan police’s specialist crime command, said: “People in the Kidbrooke area may recall seeing this man carrying a red reflective object, and possibly trying to conceal it up his sleeve. If so, please call police. He must be traced.”

The footage captures the man walking outside a block of flats in Pegler Square, close to where the body of the primary school teacher was found.

So far two men have been arrested on suspicion of Nessa’s killing but have been released pending further investigations.

The 28-year-old was attacked as she was walking to meet a friend at The Depot bar on Friday 17 September, shortly after leaving her home in Astell Road in Kidbrooke. With no apparent breakthrough in the inquiry more than a week after the body was found, pressure is building on the Met to track down her killer.

A police statement last night said that detectives, forensic officers and specialist staff were “working around the clock” to solve the crime.

However, criminologists noted the critical early stages in asuch an inquiry had passed without result and said the force would be starting to feel a “great deal of pressure”.

David Wilson, emeritus professor of criminology at Birmingham City University, said the fact that the initial stages of the case had not yielded an apparent breakthrough was significant.

“The first stages of the investigation are crucial – the first 24 hours – because in the immediate aftermath of the murder you are able to harvest a great deal of forensic evidence from the victim and the perpetrator will often have left evidence that will connect him to that murder victim. Plus you are also gathering CCTV, mobile phone records,” he said.

Police are still working on the possibility that Nessa was killed by a stranger, a fact which complicates the investigation. “If this is a stranger-perpetrated murder, it is much more difficult for the police,” said Wilson.

“The traditional way they would go about solving that crime would be looking at Facebook and the last person the victim had arranged to meet.”

Wilson, who works with numerous British police forces and is a specialist in serial killers, added: “The vast majority of murders are committed by people who knew the victim. They are in some form of relationship or have been.” The Met, he said, would have felt under huge pressure to solve the killing quickly, particularly as the case has reignited concerns about women’s safety following outrage in March when Sarah Everard, 33, was kidnapped and murdered by a Met police officer.

Hundreds attended a vigil in Kidbrooke on Friday night and yesterday a book of condolence was opened for people to pay respects to the victim.

The book is in a community centre near Cator Park, close to where the 28-year-old’s body was discovered.

It was found last Saturday by a member of the public near a walkway in the park.

Addressing the crowd on Friday evening, Nessa’s sister Jebina Yasmin Islam said she had “lost an amazing, caring, beautiful sister, who left this world far too early”.