The killing of a BBC worker and an 18-year-old murder case will be reviewed by the Crimewatch programme on Tuesday.
Mr Brown was killed the day before his 28th birthday
BBC library assistant Tom Brown, 27, was stabbed to death as he walked home in the early hours of 21 August this year in Southgate, north London.
Police have offered a £20,000 reward for information about his death - just one day before his 28th birthday.
Crimewatch will also reveal new leads in the murder of Lancashire businessman Nigel Bostock in his own home in 1986.
The 31-year-old was strangled and stabbed six times at his home in Banks, near Southport, on 20 December.
An anonymous letter relating to Mr Bostock's murder was sent to Southport police 12 months ago.
They now want the letter writer to get back in touch.
Police received an anonymous letter relating to Mr Bostock's killing
Detective Superintendent Mick Turner of Lancashire Police said: "Thanks to information uncovered during the forensic review we now have reason to believe that [the letter] could be significant to the inquiry."
Police will also reveal specific details of cord tied by Mr Bostock's killer.
Crimewatch will show a reconstruction of both murders on Tuesday.
In the murder investigation of Tom Brown, police will also show CCTV footage of the incident and of the man who called emergency services.
The BBC worker left his friend's house at about 0300 BST and walked along Southgate High Street before being attacked outside Chandos Court on The Green.
Police have ruled out robbery as a motive for the attack, as he still had his wallet and phone with him when his body was discovered.
Det Ch Insp Keith Garnish said: "Southgate High Street is a busy road and we are certain that someone must have seen something on the evening Tom was attacked.
"We are also keen to trace anyone who may have contacted the emergency service to request help for Tom and anyone who visited the cab office, Crown Cars, along Southgate High Street."
The Met has issued an e-fit of the suspect who is described as white, of slim build with a gaunt looking face, about 5ft 10in tall with light brown hair, short at the sides and longer at the front.
He was scruffy in appearance and was wearing either a grey or white hooded tracksuit top.
Police are also appealing for two other people, a man and a woman, who were seen sitting on a wall at about 0400BST 10 yards from the from where Mr Brown was killed.
The murder of a seven-year-old girl and a 41-year-old man will also be featured on the same Crimewatch programme.
Toni-Ann Byfield from Birmingham was shot alongside Bertram Byfield, 41, just over a year ago at a flat in Harlesden, north west London.
Police believe Mr Byfield, a convicted drug dealer, may have been killed over a drug debt.
The Crimestoppers number is 0800 555111.