When Katya Girenko answered the door of her family's rundown St. Petersburg apartment early one Saturday morning in mid-June, she saw two teenagers through the peephole. They asked if they could speak to her father, Nikolai Mikhailovich. When he went to the door and asked what they wanted, a gunshot rang out. The bullet smashed through the flimsy door and ripped into Girenko's chest, killing him almost instantly.
At first glance, Girenko might seem an unlikely target for assassination. A tall, somewhat fragile 64-year-old with a bushy gray beard, he was an ethnographer and anthropologist who earned his...