Tennant’s Litvinenko is essentially the sole witness to his own murder.

She would say herself, she’s dedicated her life to making sure this story is out there.

She does not want Sasha’s life to have been in vain.

DAVID TENNANT as Alexander Litvinenko

David Tennant in ‘Litvinenko’.ITVX/Sundance Now

And that’s what Putin wanted.

Putin wanted to shut him up and he failed on that front."

Tennant’s portrayal of Litvinenko mostly takes place on what would tragically turn out to be his deathbed.

DAVID TENNANT as Alexander Litvinenko, MARGARITA LEVIEVA as Marina Litvinenko

Temirlan Blaev, David Tennant, and Margarita Levieva in ‘Litvinenko’.ITVX/Sundance Now

What was it like filming those sequences?

“It felt very precious,” he says.

Margarita was just extraordinary because she just became Marina.

You know, she physically became her.

She really went to some very difficult places, she did not shy away.

I think it really counts.

I just think it’s such an important story to tell.

All episodes ofLitvinenkowill debut Dec. 16 on AMC+ and Sundance Now.

Watch an exclusive clip from the show below.