The single-car crash that killed disabled Petaluma teenager Danny Cox in August and stunned the community was ruled a suicide Friday by the Marin County Sheriff's Office.

Cox, 19, died Aug. 7 after his Dodge Magnum wagon struck an oak tree next to Highway 101 near Olompali State Historic Park.

The former Petaluma High track star had just started to drive after suffering devastating injuries in a shallow-water diving accident a year earlier — on Aug.11.

His accident left him paralyzed below the chest and he chronicled his treatment and the difficulties that he faced through Facebook and his web- site. His parents, who operate a popular restaurant in Petaluma, were open in discussing his trauma and many felt a personal connection with him.

He was able to drive thanks to a modified car he could control with his hands. Witnesses to the crash said Cox was traveling between 60 and 70 mph before hitting the tree. No skid marks were found to indicate he attempted to brake.

The findings by the Marin County Coroner and the Marin office of the CHP concluded that Cox's death was a suicide, but provided no explanation. Officials were not available for comment Friday.

His mother, Maureen McGowan, dismissed the notion her son wanted to die, though she alluded to the toll of the diving accident a year earlier.

"A broken neck took the life of my son," she said Friday night. "He died as the result of catastrophic injuries from the diving accident, absolutely that's what killed him."

Prior to the accident, Cox had been a gifted long-jumper, leaping 21 feet and placing 11th in the state high school sectionals in Berkeley.

After graduating from high school in 2010, he was on the cusp of starting his first semester at Santa Rosa Junior College, where he planned to pursue a career in firefighting, when the spinal injury turned his world upside down.

Cox's plight moved the hearts of many. His family, friends, teammates and former classmates rallied behind him, as did the greater Petaluma community, which raised tens of thousands of dollars to help with mountainous medical costs.

Last October, he got a standing ovation at his homecoming from a spinal rehabilitation center at the annual Carousel Fund Casino Night.

Wearing a black athletic suit, Cox rolled his wheelchair onto the stage at the Petaluma Veterans Memorial Building as hundreds of guests in evening gowns and tuxedos cheered and clapped. "We love you Danny," yelled one guest.

Cox smiled, saying only a few words: "Have a great night everybody."

During his treatment, his progress could be seen in frequent videos and updates posted on YouTube and on his website.

Prior to his accident, he was a fan of social networking sites like Facebook and he remained open and candid in public updates from his hospital bed and wheelchair.

He mentioned getting a wheelchair, but being in trouble for speeding in the hallway: "I would run into people. ...It's funny. But they didn't think it was funny."

At other times, he talked about the difficulty of being so helpless that others have to bathe him.

About a month after the accident, his spirit sank to new lows in a brief posting: "It's just another day. Not much has changed. Still miserable. Nothing really happened today."