Pro-democracy protesters rallying in Washington this summer against the brutal Syrian regime sometimes noticed a middle-aged man with a camera who arrived in a hulking Hummer.
Days later, thugs in Syria arrived at their relatives' homes in Syria, and dragged people away. One American dissident had her father killed.
Others tell grim tales of vicious beatings and disappearances.
The man in the Hummer, Mohamad Anas Haitham Soueid, 47, a Syrian-born American citizen now faces charges that he secretly worked for the feared Mukhabarat, Syria's secret police, gathering information on dissidents active in America as part of an effort to "silence, intimidate and potentially harm the protesters."
The arrest lifts the lid on another dark side of the desperate efforts by Arab authoritarian regimes to hang on to power as Arab Spring uprisings sweep the region.
"The ability to peaceably assemble and protest is one of the oldest rights in this country, and so the fact that you have an agent for Syrian intelligence who is working with the Syrian government to identify and intimidate U.S. citizens and others is an extremely serious allegation," said Neil MacBride, the U.S. government prosecutor.
Military units and the notorious Mukhabarat loyal Syrian dictator Bashar al-Assad have sought to crush the pro-democracy movement with brutal, violence, killing more than 2,900. For months, rights organizations have warned that Syrian agents have infiltrated protest groups overseas and spies were identifying leaders so their families could be targeted.
President Barack Obama has been ramping up pressure on the Assad government . "This desperate effort to monitor protesters in the United States shows that the Assad regime is grasping for any means to silence those speaking out against their brutal crackdown on peaceful protesters," said Tommy Vietor, a spokesman for the White House's National Security Council.
Mr. Soueid, who lives just outside Washington across the Potomac in Virginia, is accused of sending video and audio tapes to Syria. In June, he visited Damascus and had a private audience with President Assad, a surprising indicator of just how important the regime regarded targeting opponents abroad.
In Washington, the Syrian embassy denied it was secretly financing agents to spy on protests. The accusations are "baseless and totally unacceptable," all part of a "campaign of distortion and fabrications," the embassy said.
The arrest of Mr. Soueid, a car dealer, was almost lost in the furor over the brazen plot involving another American car salesman, Manssor Arbabsiar, accused of trying to hire Mexican drug cartel hitmen to stage a terrorist attack financed by elements of the Iranian government.
But both shed a little light on the bizarre, sometimes vicious, cloak-and-dagger, schemes being played out on American soil.