'Putin's Shadow Army:' What Is Russia's Mercenary Wagner Group?

Experts expect the Wagner Group will supplement Russia's military forces in Ukraine as the invasion continues.

It’s called Vladimir Putin’s shadow army, and it’s done his dirty work before. 

In 2014, the Wagner Group entered Ukraine undercover, destabilizing the eastern Donbas region and helping to seize Crimea. 

Now 1,000 mercenaries from the private Russian military company are massing in Ukraine, according to U.S. and British intelligence.