An 88-year-old white supremacist shot and killed African-American security guard Stephen Tyrone Johns at the U.S. Holocaust Memorial Museum in Washington D.C. Wednesday, just before being shot by return fire from two other guards.

Two suspected neo-Nazis who planned on assassinating Sen. Barack Obama and murdering over 100 African-Americans have been arrested by federal agents, according to the Bureau of Alcohol, Tobacco and Firearms.