Police agencies in Los Angeles and Corona are investigating the circumstance of a shooting inside a Costco Friday night by an off-duty LAPD officer who said he was assaulted while holding his young child.The shooting which sent scores of panicked shoppers running and prompted a huge police response left one man dead and two of the mans relatives in critical condition, authorities said.Later, however, police said no one was in custody and that there had not been an arrest in the case.