Marianna Mitchem grew up in the Denver suburbs, where she played high school soccer. One day in April 1999, her team faced off against a nearby rival, Columbine High. The next day, two teenagers went on a shooting rampage at Columbine, killing more than a dozen people. The massacre left an imprint on Mitchem. After graduating from Providence College, she joined the Bureau of Alcohol, Tobacco, Firearms and Explosives.