Toni-Ann was staying with her father for the weekend

Toni-Ann Byfield and her father Bertram, 41, were found in a bedsit in Kensal Green on 14 September after neighbours reported hearing shots and a scream.

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

Police said a 43-year-old man and a woman, aged 37, who had been detained in north-west London, have been bailed to report to police stations on 10 December.

A 23-year-old man and a woman, aged 28, arrested in September in connection with the inquiry have been released on police bail.

Toni-Ann spent her last day shopping for a school uniform

Toni-Ann's Jamaican mother Rosalyn Christine Richards made emotional appeals for help in solving her murder.

The seven-year-old girl was in the care of Birmingham City Council social services when she went to stay with her father, a convicted drug dealer.

The council has promised a thorough review of the management of her care.

Toni-Ann normally stayed with relatives in London during the week and often visited her father for the weekends.

Mr Byfield, a Briton raised in Jamaica, served nine years in a British prison for dealing crack cocaine and survived a similar shooting a year ago.

According to a post mortem examination he died after being shot twice and Toni-Ann was shot once in the back.

Police are continuing to appeal for witnesses.

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