(CBS News) BALTIMORE, Md. - U.S. forces are facing a growing danger: attacks by Afghan allies.
Since January 2007, 88 NATO troops have been killed by Afghan security forces. CBS News National Security correspondent David Martin spoke with the family of one fallen U.S. soldier.
Army Major Robert Marchanti had a family photo on his desk when he was killed last February. The Afghan policeman who shot him and Lieutenant Colonel John Loftis from behind probably saw it. Marchanti's wife Peggy Marchanti -- who was at the head of his funeral procession -- was so shattered it took her some time to comprehend the killer was not the enemy but a supposed ally.
"The pain, the tragedy involved is what it is," Peggy told CBS News. "But it does make it ... it just does sting a little bit more that it was by the same people he was trying to help and that he trusted."
"If he would have known he wasn't safe, then he would have been able to fight for himself. I just don't think he had the opportunity," daughter Leah Marchanti said.
Marchanti and Loftis were working at a heavily guarded building in Kabul which is frequently visited by officials, including Defense Secretary Leon Panneta.
"I thought that was a very safe place," Peggy said. "I thought that was the safest place you could probably be in Afghanistan."
Their deaths happened three days after American servicemen mistakenly burned copies of the Quran they had confiscated from enemy prisoners. Everybody was on high alert for trouble.
"The last time I talked to him he said he was in lockdown so I went to bed thinking, you know, he's safe," Peggy recalled.
Marchanti and Loftis worked behind a door protected by a combination lock, but the door was somehow open and the Afghan policeman was able to simply walk up behind them -- and then make his escape.
"He killed them both and closed the door behind him and walked out. How he got out... he must have gotten help. Some people have been arrested. Some people have been let go," Peggy said, and added that she thinks it may have been a conspiracy.
Peggy said that killer himself is gone.
U.S. investigators told Peggy that her husband's killer fled to Pakistan after the shooting. She had the flag which draped his casket when it came home, but as long as his killer remains in Pakistan she knows she is unlikely to get justice.