A few hours after meeting a former KGB general outside a spy museum here, an outspoken critic of the Kremlin became engulfed in the kind of intrigue he studies when he was shot Thursday outside his suburban Maryland home.

The shooting occurred four days after the critic, Paul M. Joyal, warned on “Dateline NBC,” the television news magazine, that a “message has been communicated to anyone who wants to speak out against the Kremlin: ‘If you do, no matter who you are, where you are, we will find you and we will silence you in the most horrible way possible.”