CCTV footage appears to show the man holding a reflective red item on Pegler Square on September 17, it is believed.
DCI Neil John, from the Met’s specialist crime command, said: “People in the Kidbrooke area last Friday may recall seeing this man carrying a red reflective object, and possibly trying to conceal it up his sleeve.
“If so, please call police.”
Detectives, forensic officers and specialist staff from across the Met continue to work around the clock to investigate the 28-year-old’s murder.
The 12-second clip of Pegler Square was released as part of a public appeal on Thursday and Friday.
DCI John continued: “Please share the CCTV footage on social media and, especially if you have connections to London or Kent.
“Show the image to family members and friends who may not have seen it. He must be traced.
“We all saw at yesterday evening’s vigil, the impact that Sabina’s death has had on the community. I would reiterate my plea to those in the local area to think and if you have any information that could help this investigation, then please get in touch.”
A 38-year-old man and a man in his 40s have been arrested and released under investigation.
Officers are content that neither of them is the man shown in the CCTV footage and say detectives “urgently need the public’s help to identify this man.”
Friends say Ms Nessa was planning to start a new life in the Middle East and teach children in the UAE or Dubai.
It is thought she was on her way to her first date after breaking up with her ex partner on the night she was attacked, LBC reports.
Londoners attended a candlelit vigil and stood together in solidarity in memory of the primary school teacher on Friday evening.
Her sister Jebina Yasmin Islam paid an emotional tribute to Ms Nessa at the event, held in Pegler Square.
She said: “Words cannot describe how we are feeling. It feels like we are stuck in a bad dream and can’t get out of it.
“Our world is shattered. We have simply lost the words. No family should go through what we are going through.”
The Duchess of Cambridge is among those who have expressed their sadness for Ms Nessa’s family.
London Mayor Sadiq Khan has called for misogyny to be made a hate crime in the wake of horrific murders of women on the capital’s streets and parks.