Near the end of the car chase, Doug originally said "Jesus" after first seeing Oerstadt's face. This caused the audience at the first preview screening to erupt into laughter, as Jim Caviezel, who played Oerstadt, is famous for playing Jesus in The Passion of the Christ (2004). This unintentional reference had gone overlooked by director Tony Scott; he had the line removed from the film before its release.
Scriptwriters Terry Rossio and Bill Marsilii didn't feel Tony Scott recaptured everything in the screenplay. They felt he was more interested in the action scenes rather than the intricacies of time travel. They wrote a plot that was airtight, but in Scott's hands the finished product is now filled with plot holes. Rossio was so disillusioned with Deja Vu (2006) he's never seen the film. Scott also admitted he did a mediocre job directing the film, but blamed that on the 19-week production schedule, which wasn't as long as he wanted.
While working on the film, first assistant cameraman Michael S. Endler learned that his father, Gerald Endler, had died. As a tribute to Gerald, a former special effects technician who had actually worked with many of this film's effects crew decades earlier on other projects, Michael was allowed, on the day of shooting the ferry explosion, to place some of his ashes on a gasoline-filled water jug that would be blown up as part of the pyrotechnics of the sequence (which was referred to on call sheets as the "Stumpf Ferry Gerald Endler Memorial Pyro Blast").
The movie went through pre-production in New Orleans. Just weeks before production was to begin, Hurricane Katrina devastated the city. With the location in ruins, the movie made the decision to find a new location to shoot. Weeks after the decision, canceling the movie altogether was in talks. Finally, three months after the hurricane, the film returned to New Orleans, Louisiana and began pre-production once again.
The third time Denzel Washington and Tony Scott have worked together. They would collaborate on two other films before Scott's death in 2012. Its also the first film Scott, Washington and producer Jerry Bruckheimer have worked on since Crimson Tide (1995), and the last film Scott and Bruckheimer would work on after six collaborations.
The Lab set was built on a sound stage in Los Angeles by production designer Chris Seagers. Seagers wanted to combine a raw-edged, high-tech feel in which everything is digital and state-of-the-art; yet have exposed cables, wires, and ducts to provide a sense of reality.
The ATF is the Bureau of Alcohol, Tobacco, Firearms and Explosives in New Orleans. It is a unique law enforcement agency in the United State Department of Justice. They are protecting the communities from violent criminals, criminal organizations, the illegal use trade of firearms, the illegal use and storage of explosives, acts of arson and bombings, acts of terrorism, and the illegal diversion of alcohol and tobacco products.
The cast and crew of the movie who did not live in the immediate area stayed at two of New Orleans' signature properties, the Renaissance Pere Marquette and the Renaissance Arts for the duration of the filming.
The crew also worked with the city's New Orleans EMS using their EMS units old and new. The EMS personal were also hired to play background extras. All but 3-4 of the EMS personnel seen in the movie are Real NOEMS personnel. The entire EMS personnel wore their own uniforms. Also the Director of EMS was used as the EMS consultant.