DONETSK, Ukraine—I was talking to some young black-clad pro-Russian agitators at a checkpoint they’d set up on the outskirts of this city in eastern Ukraine when a shiny black Mercedes pulled up a few yards away. Some of the men from the group walked over and stuck their heads into the car. I couldn’t see who the capo was, couldn’t hear what orders he was giving, but the scene was like something from a movie about the mob. Nobody wanted to say who that was in the car. Nobody wanted to repeat what he’d said.

Such scenes are increasingly common in this contested part of Ukraine near the Russian frontier. “Bosses are starting to appear on the fringes of the protests, they are middle-aged, older and better dressed than the younger men who are in the vanguard of the protests,” says Diana Berg, a 34-year-old graphic designer. The grassroots agitation in favor of Russia has become less spontaneous and more focused in recent days.

Before and since Russia’s move to annex the Crimea, many who favor the pro-European government in Kiev have argued that these “bosses” might be provocateurs from Russia’s FSB intelligence service or Spetsnaz special forces infiltrated into Ukraine to orchestrate pro-Russian sentiment. But Berg, an organizer of the pro-Ukrainian rally last week where pro-Russian thugs stabbed a student to death, says there’s a different and in some ways more frightening explanation: the ominous hand of organized crime.