An off-duty police officer inadvertently was "trapped" in a suburban cul-de-sac without backup before he shot Chargers linebacker Steve Foley, a prosecutor said Thursday. Aaron Mansker, an officer with the Coronado Police Department, had decided to drop his pursuit because no other officers responded to his calls for help, but found himself blocked Sunday morning in the dead-end street where Foley lives, said San Diego County Deputy District Attorney Jim Koerber.