Karla Homolka was played by Laura Prepon, who starred in the Fox sitcom "That '70s Show" as Milwaukee teenager Donna Pinciotti. The sitcom ran from fall of 1998 until 2006. Prepon also appeared in the feature films "Slackers" and "Come Early Morning," as well as the made-for-TV movie "Romancing the Bride." A native of New Jersey, Prepon also lent her voice to the Fox animated shows "King of the Hill" and "American Dad." After "That '70s Show" ended, Prepon starred in the short-lived series "October Road" and guest-starred in TV series such as "House," "Medium," "How I Met Your Mother" and "In Plain Sight."
The role of Paul Bernardo was played by Misha Collins, a Boston native who later went on to play an angel named Castiel in The CW's "Supernatural." Although Castiel is perhaps his best-known role, Collins has numerous film and television credits. In addition to "Karla," Collins has appeared in such films as "Girl, Interrupted" and "Over Her Dead Body." His list of TV credits is far more extensive, including guest spots on "ER," "CSI: Crime Scene Investigation," "Charmed," "NYPD Blue," "24," "Without a Trace" and many others.
Patrick Bauchau played Dr. Arnold, the psychiatrist who treated Homolka in prison. Baucha, a Belgian, began his career in the French New Wave cinema of the early 1960s. He has appeared in an many films, including 2002's "Panic Room." Another key member of the cast was Cherilyn Hayres. Hayres played Homolka's sister, Tammy, who was murdered by Homolka and Bernardo.
Although set in Canada, "Karla" was filmed the U.S. due to the sensitivity of the subject matter and concerns that the film was sensationalizing the crime. According the Internet Movie Database (IMDb), Collins eventually regretted his participation in the film and reportedly tells people not to watch it. Prepon, a natural brunette, dyed her hair red for her role in "That '70s Show," and then dyed it blonde to play Homolka. The producers of the sitcom liked the blonde look so much that they asked her to keep it for the show. Prepon's character was a blonde for the show's final seasons.