Toni-Ann Byfield and her father Bertram were killed last September

Toni-Ann Byfield and her father Bertram, 41, were found dead in a bedsit in Kensal Green, north-west London, four months ago.

Detectives believe Toni-Ann, who was shot in the back, may have been killed to stop her identifying the gunman.

It is thought Mr Byfield had been involved in the supply of drugs.

This is an investigation into murder, not drugs. This is your chance to help Detective Chief Inspector Neil Basu

And that he may have been killed over a drug debt he had previously tried to collect.

Police said the 41-year-old visited Jamaica in June 2003, where he is commonly known as Anthony Pinnock.

'Ruthless murder'

On Friday Detective Chief Inspector Neil Basu said: "Did you know what was happening in Bertram Byfield's life prior to his death? Do you know what Bertram was doing in Kingston, Jamaica, or Montego Bay, Jamaica, in June 2003.

"You may be a member of the public, or a member of the criminal fraternity. You may have been involved in an illegal transaction with Bertram. This is not the focus of our investigation."

He added: "If you feel strongly about this ruthless murder, then let me reiterate. This is an investigation into murder, not drugs. This is your chance to help."

A reward of up to £20,000 is being offered for information which leads to identification and arrest.

Anyone with information is asked to call police on 020 8733 4704 or Crimestoppers anonymously on 0800 555 111.