On the snowy set, Zellweger was spotted wearing a fat suit with obvious face prosthetics. She donned enormous pants and a puffy white jacket with matching fur-trimmed snow boots while holding a supersized "Chill Chugz" drink cup (and not the cool kind).

Her strawberry blonde bob completed her transformation into Hupp, who is receiving a life sentence for the 2016 murder of Louis Gumpenberger. She took an Alford plea, which means she escaped the death penalty without admitting culpability to the crime, according to NBC News.

Hupp was also charged with first-degree murder three months ago in the death of Betsy Faria, who was stabbed to death in 2011. Hupp has vehemently denied any role in her assassination. 

According to NBC News, Betsy, who was dying of illness, amended her life insurance policy four days before she was assaulted, handing her $150,000 policy to Hupp rather than her husband. Betsy was "murdered for the insurance money," according to Lincoln County Prosecutor Mike Wood.

The Thing About Pam, based on Dateline's true-crime podcast, stars and is executive produced by Zellweger. Joel Schwartz, Russ Faria's defense attorney, is played by Josh Duhamel, who recently joined the cast.

Zellweger revealed why she was intrigued by the story of Betsy Faria in a recent interview. "It goes beyond simply the strangeness of the narrative or the boldness of everyone involved," she explained. "It's a stark representation of current societal concerns," says the author.

Zellweger, who is dating Ant Anstead, said she wanted to talk about how societal prejudice and hidden personal motivations play a role in the American judicial system. "It also speaks to, I guess you could call it, white lady privilege in America," she continued. "And also it kinda has an interesting look at the sad invisibility of middle-aged women in America and how in the most bizarre circumstances it can work to someone's advantage, as is probably the case in Pam Hupp's story."