MADRID A car bomb blamed on the Basque separatist group ETA killed one policeman in Spain's northern Basque region and injured another on Friday after the officers were lured into a trap, Reuters quoted officials as saying. The rare attack on the Basque region's own police force, coming at the outset of the campaign for May 13 Basque elections, followed a recent crackdown on ETA that has led to a string of arrests, including the capture of its alleged top military leader in France.