Following an investigation, the NTSB concluded that the system was partly to blame because it allowed drivers to use Autopilot in an environment it wasn't designed to perform in.
"In this crash, Tesla's system worked as designed, but it was designed to perform limited tasks in a limited range of environments," Christopher Hart, NTSB member, said.
"Tesla allowed the driver to use the system outside of the environment for which it was designed, and the system gave far more leeway to the driver to divert his attention to something other than driving."
Previous reports that Mr Brown was watching a Harry Potter film at the time of the collission were dismissed, and the NTSB revealed that neither Mr Brown, or the truck driver, were under the influenc of drugs or alcohol, nor were they fatigued, at the time of the crash.
It also found that Mr Brown's inattention, and the truck driver's unwillingness to give way, were primary factors of the incident. A previous NTSB report stated that while Mr Brown was driving for 37 minutes, he had his hands on the wheel for just 25 seconds.
Still, Tesla released a statement welcoming the NTSB analysis and pledged to evaluate the recomendations, including steps to limit the use of system in situations it is not designed to operate in.
Read More: BBC News