The daughter of ISIS victim David Haines is travelling to the US this week to make a personal plea at the trial of El Shafee Elsheikh for the terrorist group to reveal where her father's body is buried.
Mr Elsheikh, one of the alleged British ISIS 'Beatles' members, is due to stand trial for the murder of 28 hostages in Syria in 2014 and 2015.
The 33 year old from west London, who denies the charges, is one of the most senior ISIS members to be prosecuted.
Ms Haines's father was a humanitarian aid worker in Syria when he was abducted in 2013 and later murdered.
The group later released footage of his killing.
Ms Haines, 24, is travelling to the US to attend Mr Elsheikh's trial in Alexandria, Virginia, and has written a victim impact statement about her family's ordeal which she intends to read to the court if he is convicted.
Mr Elsheikh is not charged with Mr Haines murder due to the lack of US jurisdiction but she intends to ask him to “do the right thing” and reveal her father's final resting place.
“Don’t do it for me,” she intends to tell him. “Do it for my son, so that he can finally say goodbye to his grandad.”
“I’ve prepared for this for years,” she told The Sunday Times. “I want to be able to see him at all times; to see his facial expressions.”
Ms Haines told The Telegraph she wants to make it clear to the court that ISIS atrocities had "nothing" to do with religion.
“When it first happened, I was young and naive. I thought: Christians don’t go around doing this stuff," she said.
Ringleader of the Beatles terrorist group Mohammed Emwazi was killed in a US drone strike in Raqqa.
In Turkey in 2017, Aine Lesley Davis was sentenced to seven years in prison. Alexander Kotey pleaded guilty in the US last year and is awaiting sentence.
The UK agreed to hand over a wealth of operational intelligence on Kotey and Mr Elsheikh in return for a promise from the US Department of Justice to drop the death penalty in the case.
The UK does not have capital punishment and a British court had prevented co-operation in the case if the men were to face possible execution if convicted.
