ALEXANDRIA, Virginia - C. Lee Hanson was on the phone with his son - a passenger on United Flight 175 on September 11 - and heard him say "Oh my God!" just before watching his son's airplane crash into the World Trade Centre.
Hanson's testimony at the sentencing trial of September 11 conspirator Zacarias Moussaoui was one of several emotional stories told by survivors or sobbing family members of victims of the deadly hijackings.
Hanson, 73, said he received two phone calls from his son Peter, who was travelling to California with his wife and 2-1/2-year-old daughter on September 11, 2001.
"On the first call, he told me the plane had been hijacked. He asked me to call United Airlines and tell them," he said.
Hanson said he called the local police after being unable to get through to the airline. Then, his son called again.
"He said it was a very bumpy ride. People were throwing up all over the place," Hanson said. "He said, don't worry dad -- if it happens it will be quick."
"As we were talking, all of a sudden he stopped and said 'Oh my God, oh my God, oh my God.' I thought I heard a woman scream.
I looked over at the television set and saw a plane fly into the building."
Hanson's story, like that of the other witnesses who testified, was presented by prosecutors who want the jury to give Moussaoui a death sentence for his crimes.
Moussaoui has pleaded guilty to six counts of conspiracy in connection with the September 11 attacks. The jury will decide whether he will be executed or sentenced to life in prison.
Before the jury came into the courtroom on Monday, US District Judge Leonie Brinkema warned prosecutors about using overly emotional testimony or making witnesses too upset.
"The government is approaching shaky ground," she said. "The prejudicial impact ... might affect the rationality of the verdict. You may pay a price for that down the road."
Prosecutors played a 911 emergency call made by a woman who was trapped on the 83rd floor of the World Trade Centre's south tower on September 11.
"It's very, very, very hot," Melissa Doi frantically told the 911 operator. "All I see is smoke. I'm going to die, aren't I? I'm going to die, I know I'm going to die."
The operator tried to calm her, saying that rescue workers were trying to get people out of the building. The woman could be heard yelling "Help! Help!" at the end of the tape.
Several witnesses broke into tears on the stand. One woman cried as she talked about her two brothers, employees of Cantor Fitzgerald, who died in the World Trade Centre.
Ronald Clifford described helping a severely burnt woman after the first plane hit the World Trade Centre. He said he sat in the lobby of the building and prayed with her as the second airplane crashed into the World Trade Centre.
He only realised later that his sister and niece were on that second airplane.
Harry Waizer, who ran Cantor Fitzgerald's tax department on September 11, spoke of beating out flames in an elevator and getting hit by a "fire ball" that left him severely burnt. He spent five months in the hospital and listed a long list of problems that still plague him.