A security guard at Washington's Union Station on Friday fatally shot a man who had allegedly stabbed a woman in what police believe was an incident of domestic violence."We believe this is a domestic-related incident," Metropolitan Police Department's Jeff Brown told reporters. "Obviously with this being 9/11 fears were heightened."The suspect died at the hospital, police said. The woman was being treated for her injuries.Security had been beefed up around the US capital on the anniversary of the Sept. 11, 2001, attacks on the World Trade Center twin towers in New York and the Pentagon.