Shafilea Ahmed's younger sister saw her parents suffocate her by forcing a bag into her mouth and putting their hands over her head "to close her airways", a court hears.
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Iftikhar and Farzana Ahmed are accused of killing their 17-year-old daughter Shafilea in the family home in September 2003.
The murder was allegedly witnessed by Shafilea's younger sister Alesha, who kept the secret for seven years.
Today Andrew Edis QC told Chester Crown Court: "She (Alesha) describes what is an act of suffocation by both her parents acting together."
He said they put their hands over her face "to close her airways so she could not breathe."
He added: "She had a bag forced into her mouth."
'Wrapped body up'
Mr Edis said Alesha will tell the court how she saw her parents in the kitchen of their home in Liverpool Road, Warrington, with bin bags and tape, wrapping the body up.
She told police she later saw her father outside.
Mr Edis said: "She looked out of the window and saw her father with a large object wrapped in bin bags. She assumed that was the body of her sister."
He said she then heard a car driving off.
'Final piece of the puzzle'
Shafilea's decomposed remains were discovered in Cumbria in February 2004 but it was not until 2010 that her sister Alesha provided the "final piece of the puzzle" about her death, the court has heard.
Ahmed and his wife, aged 52 and 49, both deny murder.
A couple allegedly murdered their "westernised" teenage daughter because they believed her conduct was bringing shame on the family.
Mr Edis told the jury that Alesha was arrested in 2010 for being involved in a robbery at her parents' home, in which three masked men tied up her mother, two sisters and brother.
Six days later she alleged to police that her parents killed Shafilea, he said.
Mr Edis told the jury Alesha was either telling the truth about the death of her sister "which she has kept under wraps for years for reasons of family loyalty" or for other reasons because her relationship with her parents "became toxic".
Mr Edis said Alesha, who is on witness protection, was awaiting sentence on the robbery charge, and added: "She hasn't received any promises or indeed any inducement prior to when she first made these allegations."
He described her disclosure as a "bombshell" and said it was either the truth or "a wicked lie made up to help herself".
He added: "She now finds herself estranged from the family as a result of what she has said. Her life has turned upside down because of what she has said and what she has done."
The case continues.