It's a day every American will remember in some form, but for some like Kirkwood native Warren Nelson and his wife Betty, Sept. 11, 2001, is the day their lives changed forever.
"We were glued to the TV throughout the day, worried, hoping and praying," Nelson said. "I try to compute in my mind how long it might take David to walk down the 92 floors."
Fifteen years later, Warren relives the painful moments before learning his son David was killed in the World Trade Center.
"We just will never forget that terrible day," he said.
At the time, his son David was working in his office on the 92nd floor of the North Tower.
Warren said his son was on the phone with one of his customers from Saudi Arabia when American flight 11 hit the building.
"He said the phone just went dead while David was talking," Warren said.
Unable to make it down to a safe floor, David and 68 others in his office were killed.
Warren, a World War II vet, said he's he's been forced to overcome many obstacles in life, like seeing his own friends shot down.
"This with David is something we will never get over," he said.
David was a 1969 graduate of Kirkwood High School. He left behind a wife and two children, just 4 and 8 years old at the time.
Now 19 and 23, they are the two reasons why Warren says he's determined to keep his son's memory alive.
"This book has been difficult to write," he said.
A few years ago, Warren wrote "Swedish Men don't Cry" for close relatives and loved ones.
The unpublished memoir describes his son's passion for being a family man and his love for running and playing the horn.
"I thought later in life they'll be glad they have this," he said.
As a way for friends and classmates to honor David Nelson, a memorial for him was was set up in Queeny Park. There a plaque and bench sit underneath a tree that stands tall in his honor.