JEFFERSON COUNTY, Colorado — The passage of time has an impact on all things, especially tragedy.

"At times, it seems like it was just yesterday and then other times, it seems like it was in a far distance," former principal Frank DeAngelis said. 

Over time, victims like Craig Scott said grief evolves. He watched as two friends were shot and killed in the library before finding out that his sister was also killed.

"I know myself that in my process after Columbine there were times I was very angry that there were times I was very depressed and very sad," Scott said.

Twenty years later, Tom Mauser wears the shoes his son Daniel was wearing when he was killed.

"There are two lives you've lived," Mauser said. "There's the before and after the tragedy. It's just a totally different life for you. You measure things by whether it happened before or after that day."

That day stopped time for the victims.

"I just think of the kids who lost their lives and who they would be today," DeAngelis said. "What they would be like today and I think that's something that remains with me for the rest of my life."

Mauser says he can't afford to think like that. He still sees Daniel as a 15-year-old boy.

"For a number of years, Daniel's best friend would come once or twice a year to visit us and I had a real, real problem with that," Mauser said. "My wife was very accommodating and welcomed him. I had a tough time with it. It wasn't that he did anything wrong. I appreciated what he was doing, but it was really tough to see him growing and moving along. It took at least a good 10 years to get over that."

Scott says it took long time him to move past April 20, 1999.

"Columbine definitely had a big impact on my identity because a lot of the world saw me as being a Columbine survivor or being oh he lost his sister, oh he saw that," Scott said. "That's part of my story, but it's not who I am."

Coni Sanders lost her father, Dave Sanders that day.

"My older daughter for many, many years would say Grandpa was in the wrong place at the wrong time," Sanders said. "Ten years ago without prompting, she said he was at the right place at the right time and I think that was really an important shift for our entire family."

Dave Sanders is credited for saving the lives of dozens of students as he put himself between them and the gunmen. Coni Sanders says one day at the Columbine Memorial she met one of those students who now has a child.

"I can't even describe the feeling that creates when you're standing there holding a child knowing that yes, he died. But, he saved so many lives and now those people have families and their families will have families and it almost feels like he saved a piece of the generation," Sanders said.

Sanders says time has revealed even further impacts.

"The two shooters from Columbine actually were on Diversion. They were in trouble with the law and I now run part of the program that they went through," Sanders said. "So, in my mind, I'm kind of reversing time and saying let me help people that may be headed down a path where maybe their future would've included something horrific that would cause mass harm."

Twenty years later, the families might say they are now 20 years stronger.

"I think others feel the same sense of unity and bond," Scott said. "Every time we see each other, there's a deeper bond because of what we experienced together."

DeAngelis has a word to describe it.

"I think the reason that we're so strong today is because we were a family," DeAngelis said. "We are Columbine."

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