A measure requiring further federal investigation into the 2001 anthrax attack that killed five people was approved Thursday by the House of Representatives. It was proposed by two skeptics of a recently closed FBI probe that blamed the deadly attacks on Bruce Ivins, a microbiologist at the Army biodefense lab at Fort Detrick in Frederick. Maryland Republican Rep. Roscoe Bartlett, who represents Frederick, and Democratic Rep. Rush Holt, from the New Jersey district where the anthrax letters were mailed, want the director of National Intelligence to investigate potential foreign connections to the attacks. Ivins committed suicide in 2008 after coming under FBI scrutiny. "His colleagues say that he would not have done it," said Bartlett, who complained that Fort Detrick officials have refused to let him speak with scientists who work there. Holt said "many questions remain" about the FBI's handling of the case, including whether a foreign connection was "overlooked, ignored or not pursued."