Joy Hewer, 52, was stabbed and sexually assaulted at her own home on 17 October 1995.
The retired primary school teacher was found dead after police and firefighters were called to a blaze at the sixth floor flat in St David’s Court, off Parkstone Road, Walthamstow, at around 11.45pm.
Ms Hewer, a devout Christian, had suffered multiple injuries including a number of stab wounds.
The murder remains unsolved.
On the 20th anniversary of the case in 205, detectives and the victim’s sister renewed appeals for help tracing her killer and a £20,000 reward was offered for information leading to a conviction.
Joy was our loving sister who was absolutely no harm to anyone. We couldn’t think of a person less likely to be attacked in this way. She’d enjoyed her work as a teacher, adored her nieces and nephews and was fantastic with children. She regularly attended church and often helped at charity events.
We’ve never forgotten the moment we were told she’d been murdered. It will never make any sense to us. Joy was someone who would go out of her way to help others. She lived a quiet and peaceful life which was totally at odds with her last terrifying moments. We need to see closure and can’t face another 20 years of unanswered questions.Penny Barnes, Joy’s younger sister
Ms Hewer had visited the London Healing Mission in Notting Hill on the afternoon of her death and was seen leaving at around 3.30pm.
She visited a chemist near her home in Wood Street, Walthamstow, at 5.50pm.
At around 10.30pm a neighbour at St David’s Court heard loud noises or banging coming from Joy’s flat.
Then at 11.18pm an unidentified man dialled 999 from a public telephone box along Fulbourne Road, Walthamstow, to report smoke coming from Joy’s flat.
While on the phone the caller can be heard asking someone waiting for a bus what road they were standing in to assist the emergency call handler.
Firefighters broke into Joy’s flat to find her lying in the bedroom and extinguished two fires which had been deliberately set in the bedroom and lounge.
Police are trying to trace the unidentified caller and the person waiting in the bus queue.
Detectives are also trying to trace a man seen on CCTV entering St David’s Court at around 10.30pm. He is described as white, aged between 30 and 40 and wearing a light coloured jacket.
Detective Inspector Susan Stansfield, of the Met’s Special Casework Investigation Team, who is leading the investigation, said: “Joy Hewer was a kind-hearted Christian woman who was devoted to her beliefs and to her family.
“Originally raised in Hoe Street with her younger brother Steven, and younger sister Penny, she regularly attended several churches in the Walthamstow and Notting Hill areas.
“She had worked for many years as a dedicated local primary school teacher before retiring in 1990. Unmarried, she continued to stay close to her family and friends and worked for various charities.
“As a result of our investigations we are sure Joy would have been cautious about letting someone enter her flat late at night. There were no signs of a forced entry and it may be that she knew the person her entered her flat that night. Our forensic teams also found two used coffee cups within the address.
“After two decades we realise a lot of time has passed and someone who may have not been able to speak in 1995 may feel they can come forward now, 20 years on.
“Joy’s parents have sadly passed away but her brother, sister and nieces and nephews still very much hope to see someone brought to justice.
“We hope that this latest appeal will see someone with the final piece to the jigsaw to speak out.”
The case also featured on BBC’s Crimewatch programme on 14 December 2015.
Call the police incident room on 020 7230 7963, or call Crimestoppers anonymously on 0800 555 111.