'Constantly on my mind' - 9/11 agony goes on for bereaved, 25 years on

The US government has described it as the "most egregious criminal act on American soil in modern history".

But a quarter of a century on, the trial of its alleged mastermind is yet to begin and families of those killed fear that time for justice to be delivered is running out.

Tom Resta's brother John and his wife Sylvia, who was seven months pregnant, were among the almost 3,000 people killed on 11 September 2001 when hijackers flew planes into the World Trade Center in New York City and the Pentagon in Virginia. Another crashed in a field in Pennsylvania after the passengers fought back.

The couple had been preparing their unborn baby's nursery, painting it with characters from the children's television show Blue's Clues in the days before 9/11. They had dreamed of having a baby and doted on the children of friends and family.

On the day of the attacks, the couple - both traders - were working on the 92nd floor of the north tower of the World Trade Center.

"After all this time, it still chokes me up," Resta told the BBC through tears. While 25 years have passed, he said 9/11 was "almost constantly" on his mind.

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Resta has been to the US naval base of Guantanamo Bay four times to watch complex pre-trial proceedings for alleged 9/11 mastermind Khalid Sheikh Mohammed and his co-defendants - a process he describes as "laborious and tedious".