Fueled by an addiction to prescription painkillers, an FBI agent abused heroin from his own drug investigations and in the process botched dozens of cases involving suspected drug traffickers in multiple states, according to details that emerged Friday. Matthew Lowry, formerly a special agent with the agency's Washington field office, tampered with hundreds of grams of heroin seized during drug investigations in 2013 and 2014, keeping it in his car for weeks or months, and periodically using it, according to charging documents filed in federal court in Washington, D.C., on Friday.