The notion that highly trained assassins would be exhibiting any overt signs of stress or fear before, during, or after doing their job is beyond me.

Equally much is the notion that those people would be working under threat to their families if they did not succeed. That sounds like a good way to have disloyal assassins whom will screw you over the minute they can find a way to do so while saving their families. Much better to have someone with a Nanners-level of loyalty to their national leader, but with a personal sense of honor, whom will gladly die in service to their country.

but what do I know about Russian assassins?

I'm not taking any side in whether or not they did it.