The mother of the youth accused of murdering Midlothian teenager Jodi Jones has been accused of lying during his trial.
Mrs Mitchell was told she no longer faces criminal charges
Corinne Mitchell was challenged by the prosecuting advocate over a knife she had bought for her son Luke.
Mr Mitchell denies murdering the 14-year-old schoolgirl.
The court heard that Mrs Mitchell, who was charged by police on the day her son was arrested for Jodi's murder, will not face criminal charges.
It is alleged that Mr Mitchell killed Jodi on 30 June, 2003, in Dalkeith.
The 16-year-old, who was the teenager's boyfriend, denies the charge and has lodged two special defences, one of alibi and one of incrimination.
Mrs Mitchell, 45, smiled at her son in the dock before beginning her evidence at the High Court in Edinburgh.
She was asked why, despite realising her son was suspected of a knife killing, she had bought him a knife for Christmas. Mrs Mitchell told the court it was for camping excursions.
Prosecuting advocate depute Alan Turnbull QC, suggested it had been bought to replace one Luke had before Jodi's death.
He accused Mr Mitchell's mother of lying when she said that on returning home after being interviewed by police she remembered that the knife she had bought was hidden in a bag under the dog's feeding table.
Mr Turnbull told the court that specialist officers had already searched there.
Mrs Mitchell also told the court she could not understand why neighbours said they had seen smoke coming from her garden on the night of Jodi's death, because she had not lit the log burner that night.
She also could not understand why a range of people had seen Luke wearing a parka jacket prior to Jodi's death, when she bought him a parka jacket a week after her murder.
Mrs Mitchell said Luke was at home making dinner at about the time Jodi is believed to have been killed.
On Thursday, Mrs Mitchell told the court that she had returned to the family home at about 1715 GMT on 30 June.
She said her son older Shane was in his bedroom and her other son Luke was in the kitchen cooking dinner.
Mrs Mitchell said Luke ate his meal in the living room before setting off to meet Jodi at about 1740 GMT.
"They arranged to meet. He wasn't sure what time. All he knew was she was coming down," she said.
The body of Jodi Jones was found in woodland near her home
Mr Turnbull said: "On that account it would seem that he (Luke) couldn't have been at the Easthouses Road end of the Roan's Dyke path at around five to five?"
Mrs Mitchell said that would have been "impossible".
She said her son had returned home at about 2100 GMT and told her Jodi had not turned up.
Mrs Mitchell said that had been a surprise to her, adding that Luke had been "miffed" at Jodi's non-appearance.
Asked whether her son had seemed anxious, she replied: "Not at that point, no."
Shane Mitchell had earlier told the court that he had discussed with his mother what he should tell the police in the days after Jodi's death.
He said he was extremely shaken up and could not remember a single thing about the day Jodi was killed.
Mr Mitchell said his memory had been affected after a problem with drugs a few years ago.
He was asked by Mr Turnbull if the discussion with his mother had affected what he told the police.
Mr Mitchell said that it had, and that the statement was not accurate.
He was asked by defence QC Donald Findlay if there was any point in time where he could say he knew as a matter of fact that Luke was not in the house.
Mr Mitchell replied: "I can't say that."
The trial continues.