PALM DESERT, Calif. -

More information has been released explaining why an elderly man is being charged with a DUI in the crash that injured 10-year-old Adrian Grajeda last October, despite the man being within the legal limit to operate a vehicle.

According to documents describing the arrest warrant, 83-year-old Malcolm Paterson's blood test resulted in a BAC of .04% on the morning of October 23.

Even though .08% is the standard reading for a DUI, officers said Paterson's actions throughout the crash, combined with his BAC, led them to believe that alcohol contributed to a mental impairment making him unable to drive the car safely.

The accident happened around 10 a.m. near the intersection of Portola Avenue and Magnesia Falls Drive. Investigators determined Paterson had mistakenly pressed the accelerator instead of the brake pedal when he approached stopped traffic at the intersection.

When noticing the car wasn't slowing down, Paterson pressed down harder on the accelerator without realizing his mistake. Authorities said he ended up colliding with a vehicle, drove through the intersection facing oncoming traffic, and drove onto the sidewalk where he dislodged a traffic signal pole from its base.

Paterson's car finally came to a rest when he crashed through the steel fence at Lincoln Elementary School and ended up on the playground.

Adrian Grajeda was struck by debris from the crash and was forced to have part of his left leg amputated. Adrian received a prosthetic leg on May 2 that allows him to run again.

Paterson hasn't been arrested yet. Continue to follow KESQ and CBS Local 2 as more information becomes available.