Governments at times can and do lift diplomatic immunity if the case doesn't involve official duties. In 1997, Georgi Makharadze, deputy ambassador from Georgia to the United States, was convicted of killing a 16-year-old girl after drinking and speeding. Makharadze spent three years in a U.S. prison and two in a Georgian prison. He is now on parole.
"Diplomatic immunity is not always immutable," Burns said. "A government can decide to drop diplomatic immunity and subject a diplomat to the local law enforcement or courts of a country. ... I think it's appropriate sometimes for the government to give up diplomatic immunity if the person has committed an egregious crime of a private nature."
Modadi was on an official mission to Detroit, a sensitive one. He was going to visit jailed Qatar al Qaeda member Ali Saleh Kahlah al-Marri in a supermaximum security prison, part of his routine duties. Al-Marri was arrested in Illinois shortly after the 9/11 attacks and is believed to have been an al Qaeda sleeper agent.
Federal officials confirmed Thursday that Modadi would face no charges, saying he "absolutely will not be charged with a crime. He has diplomatic immunity. He invoked it."
A senior U.S. official said the United States and Qatar are looking for a way to bring the matter to a close without further embarrassment.
"I expect this to be resolved very quickly," State Department spokesman P.J. Crowley told reporters Thursday, without elaborating.
ABC News' Brian Hartman, Scott Mayerowitz, Kirit Radia and Jason Ryan contributed to this report.