To approach this without emotion:
If the probability that a given man is a bomber is sufficiently high (given appearance, demeanor, positive ID, etc.), he should be killed simply based on the likelihood that x lives might be lost if no action is taken. If this situation occurs multiple times, the ratio of correct assessments to incorrect ones made by the police should be taken into account and future action should be adjusted appropriately. So, really the question is: can the police effectively measure the relevant probability/threat level?