The Team Bondi head explained how the small studio's ambition saw development go on for seven years.
"One [thing] is the size, it's a huge game - probably too big. The map's massive, and so that's probably my fault," he told Official PlayStation Magazine.
"We had to build a new process to do that. We were a brand-new studio - we had brand-new tools, new technology. We have tools that allow you to build cities now, but we had to build that kind of stuff and make it work.
"Everything from the road network, where all the trolley cars go, all the cables connecting automatically to all of the buildings."
McNamara continued: "The tech was pretty extensive, including MotionScan. I'd say the first year and a half - [maybe] even longer - was just research. Newspaper research, guys going over to LA and doing research on the buildings, taking photos, getting all the resources together.
"We were quite a small studio - 16 people or something – and we had to have all this material so we could start building stuff."
McNamara recently explained why protagonist Cole Phelps would often provide over-the-top responses in interrogation scenes.
L.A. Noire placed fourth in Digital Spy's Games of 2011 countdown.
The L.A. Noire: Complete Collection, which features the original game and all DLC, is out on Xbox 360, PlayStation 3, PC and OnLive.
> Read Digital Spy's Xbox 360 review of L.A. Noire
Watch the launch trailer for L.A. Noire below: