At a key moment in Zodiac, director David Fincher’s historical dramatic thriller, the narrative takes the form of a hypnotic montage, artistically drawing together the letters and clues a serial killer has provided to investigators at a time when the officers must repeatedly return to the offices of the San Francisco Chronicle.

To create that sequence, Fincher and his collaborators, including editor Angus Wall, turned to the talented artists at LA visual effects design company A52.

The tapeless, digital post-production workflow behind Zodiac has generated a great deal of interest in both the feature film and commercial production industries over the past year. Fincher famously pioneered the use of Thomson's Grass Valley Viper Filmstream digital cinematography camera on several commercials he has directed since 2002, and he used the same camera to capture Zodiac.

"This was a perfect job for A52," Angus Wall said, "as it called for great design and the ability to take a concept and run with it. Andy, Kirk, Max and Pat really delivered, far exceeding expectations for the sequence. As one of the only purely visual flourishes in the movie, it's a rare blend of content and style. Thanks David!"

For A52, the team consisted of VFX co-supervisors Andy Hall and Pat Murphy, 3D animators Kirk Shintani and Max Ulichney, producer Sarah Haynes, and executive producer Mark Tobin. After receiving extensive input from Wall on Fincher’s vision for the sequence, high-resolution scans were taken of the actual letters from the Zodiac killer.

"It seemed early on that the process required a strong collaboration between 2D and 3D to really capture the level of detail that David was looking for," explained Andy Hall. "Working with Maya and Mental Ray, the letters were reconstructed so the camera could literally travel into the fibres of the paper."

With Hall and Murphy collaborating on the camera moves that carry the sequence through, Murphy used Autodesk Inferno to artistically composite together the CG and live-action elements. "The montage itself is very simple," Murphy explained. "We weren't trying to make it too elaborate, it was more of a visual for the audience to be able to read and understand what was happening."

Murphy also explained that, at first, the idea of the sequence was to just treat the letters as letters – to have them lie over the top and let them play across all the scenes. Wall provided the A52 team with a template of the sequence as a starting point, and then the collaboration began. As the process continued, the team found that placing the elements into the 3D space provided within the live-action plate was much more interesting. In the end, the sequence lives almost entirely in this 3D space, leaving the letters and papers in the scene as objects the actors walk both through and around.

"This was a great opportunity to collaborate with David on a design oriented project involving both 2D and 3D elements, something for which A52 is well suited," explained Mark Tobin.

According to A52’s Sarah Haynes, the raw live-action Viper footage for the sequence was provided to A52 on a portable hard drive in the form of DPX files. After A52’s work was completed, the sequence was output as DPX files and sent to Technicolor, where it was coloured by Stephen Nakamura and mastered as part of the film’s Digital Intermediate.

"Though the part we played in the production of Zodiac was small, the sequence we created turned out to be a very important story element in the film," concluded Andy Hall. "Also the amount of freedom that David Fincher allowed us to evolve the sequence was something of a rare opportunity."

Zodiac opens in the UK on May 18.