A £20,000 reward will be offered for information about the killer who stabbed a primary school teacher to death in her home 20 years ago.
Joy Hewer was sexually assaulted and left for dead in her flat in Walthamstow, north-east London, on October 17 1995.
Detective Inspector Susan Stansfield, who is leading the investigation, will announce on the BBC's Crimewatch programme that a £20,000 reward will be paid for information leading to the arrest and conviction of the murderer.
Firefighters found the body of 52-year-old Ms Hewer, a devout Christian, in her bedroom with multiple stab wounds after two fires were deliberately started in the sixth-floor flat.
The Met Police has previously appealed for information about a man seen on CCTV entering St David's Court at around 10.30pm on the night of the murder.
Ms Hewer's family made an appeal for help finding her killer, which will be repeated on the programme.
Her sister Penny Barnes said Ms Hewer was "absolutely no harm to anyone" and "would go out of her way to help others".
"We need to see closure and can't face another 20 years of unanswered questions," she added.
"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. She lived a quiet and peaceful life which was totally at odds with her last terrifying moments."
Niece Jo McCarthy will speak of how Ms Hewer's parents died without finding out what happened to her.
"I just don't think that they had any peace," she will tell Crimewatch.
Police will also release a facial reconstruction of another suspected murder victim after a skeleton was found in a ditch in a quiet country lane.
The remains, wrapped in bin bags and a blanket, were uncovered by workmen clearing an area in the village of Warfield, Berkshire.
Officers believe the skeleton, that of an adult man, could have lain in the ditch for more than two years.
Two blunt-force injuries were found on the skull, according to Thames Valley Police.
A murder investigation was launched after the discovery was made in July and officers are appealing for information to identify the victim.
Detective Chief Inspector Kevin Brown will describe the man as having a "distinctive" face with a "white and noticeable" smile.
"He has quite a strong brow line, where his eyebrows are, and that's very distinctive and would have been distinctive to anybody that knew him," he will tell Crimewatch.
"Somebody will know who this is - somebody's brother, somebody's son, maybe a father - that person will know instantly who this person is."
A digital image of what the man may have looked like will be shown along with a reconstruction of how the remains were unearthed by a digger.