COLOMBIA, Russia and Sierra Leone were the deadliest assignments for journalists last year, with conflict and crime killing three in each nation. Overall, two dozen journalists were killed in the line of duty in 2000, many of them assassinated in retaliation for their work in countries stretching from Bangladesh to Uruguay, according to “Attacks on the Press in 2000,” an annual survey by the Committee to Protect Journalists. “These are all countries where those who kill journalists in order to silence them understand that they can get away with murder.” The number of journalists killed last year was down from 34 in 1999 and even higher death totals in the early 1990s.