[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/images/06/11/intv.townsend.art.jpg caption="Frances Townsend says the 'lone wolf' represents the most difficult problem for law enforcement."] An 88-year-old Maryland man with a long history of ties to white supremacist groups is the suspect in Wednesday's fatal shooting at the U.S. Holocaust Memorial Museum, two law enforcement officials told CNN. Experts say there are an … Continue reading Commentary: "Lone wolf" most difficult threat to fight