Toni-Ann with the man she thought was her father, Bertram Byfield

Toni-Ann Byfield was shot alongside Bertram Byfield, 41, a convicted crack dealer she thought was her father, at a flat in Harlesdon, north west London.

Police believe Mr Byfield was linked to a Jamaican drug cartel and may have been killed over a drug debt.

They are appealing, in particular, for information about a white-handled bread knife found near the murder scene.

Detectives think Mr Byfield had links to the British Link Up Crew, a "ruthless" group of Jamaican crack dealers running cocaine between the UK and Jamaica.

Det Ch Insp Neil Basu said Mr Byfield, formerly known as Anthony Pinnock, was owed £25,000.

Gang hierarchy

"It is possible that Anthony was trying to elevate himself within the hierarchy of this gang or was trying to call in a debt on their behalf and was killed as a result of his actions.

"Only someone in or close to this gang will have the information I need.

"They should search their conscience, look at their own children and try and imagine how the Byfield family are feeling every day."

Toni-Ann had come to the UK from Jamaica in 2000 to live in Birmingham with a woman, thought to be her aunt, who turned out to be one of Byfield's girlfriends.