“I have the living room shut for privacy. I didn’t see anyone. The [front] door got opened. Emmerdale was still on television, but I’m not sure about exact times.

“They definitely both left together.”

Schoolboy Rhys was shot at 7.28pm, three minutes after the end of Emmerdale, as he walked home from football practice across the Fir Tree pub car park, in Croxteth Park.

The prosecution allege Mercer fired the shots at members of the rival Norris Green Strand Gang, after they strayed on to his turf.

The 18-year-old, of Good Shepherd Close, Croxteth, denies murder.

Mercer agrees he arrived at Boy K’s home at about 7pm, but claims he stayed until 8.15pm, giving him an alibi.

In the witness box, Miss K said she was no longer sure on exact times.

When Mercer’s barrister, Richard Pratt, QC, suggested Mercer, who was a regular caller at the house, had stayed until about 8.15pm, she replied: “Could be.”

She admitted she had been drinking that day, but “not as much as usual”.

Tim Clark, defending Boy M, suggested that, at 7.28pm, the time Rhys was shot dead, Mercer was not at her house and that was what she told police.

He then asked her if anyone had asked her to be less clear about times and dates since she made her statement to the police, to which she replied: “No.”

Minutes later, when asked by Paul Lewis, defending her son, if she was sure about times on the night of the shooting, she replied: “No.”