Holly Ratchford has decided to speak out publicly for the first time

Holly Ratchford still cannot believe that the man who moved into the residential complex she once managed would go on to be accused of involvement in the darkest day in recent US history.

"It's almost impossible for me to wrap my head around who he said he was, and who he really is. I still struggle with that," she tells the BBC.

The man, Omar al-Bayoumi - a Saudi in his early 40s - moved to the complex in San Diego, California, with his family in September 1999.

The new resident at number 152 Parkwood Apartments quickly became a regular at Ratchford's pool parties. "He was always so bubbly and smiling," she recalls, "and just very, very friendly."

A few months later, Bayoumi would introduce Ratchford to two apparently unassuming, "polite" men, who would also become her neighbours.

The pair would become infamous for hijacking American Airlines flight 77, and crashing it into the Pentagon, in the 9/11 attacks.

Ratchford has been haunted by her connection to these three men for the past 25 years. She feels she was taken in by Bayoumi from the start.

"Whenever I had parties he would come and be a part of the activities," she recalls, adding that his family would invite her in for food.

But Bayoumi, the one-time resident of 152 Parkwood, is now at the centre of the $1 trillion (£733bn) lawsuit brought against the Kingdom of Saudi Arabia by several thousand families of victims and as well as survivors of 9/11.