When Wendy Holland heard that a security guard was gunned down at the U.S. Holocaust Memorial Museum last June, she didn’t think much of it. She saw the clip on the evening news and went back to life as a 17-year-old in Prince George’s County: advanced classes, sports practices, hanging out with friends. Then, two weeks later, her principal came on during morning announcements at Crossland High School and called for a moment of silence for Stephen Tyrone Johns, explaining to about 2,000 students that the man who was shot and killed by a white supremacist inside the museum was a 1988 graduate of the Temple Hills high school.