OCEANSIDE - Four U.S. troops were killed over the weekend in the latest in a string of insider attacks on coalition soldiers by gunmen dressed as Afghanistan officers.The incident is heartbreaking for the family of 21-year-old Lance Cpl. Greg Buckley Jr., of Oceanside, who was shot dead by an Afghan police officer at a military base last month. The attack over the weekend happened at a remote checkpoint, U.S. officials say. A total of 51 coalition troops have been killed in the so-called insider attacks. Rep. Peter King (R-Seaford) has asked the head of the CIA to investigate and to find out what can be done to prevent further attacks. He says U.S. troops should be armed at all times and that the military needs to do a better job of vetting Afghan troops and police officers.