New York (CNN) -- Kerry Kennedy's lawyer filed a motion Friday to dismiss her case, saying the daughter of the late Sen. Robert F. Kennedy did not knowingly ingest a sleeping pill before causing a traffic accident in Westchester County, New York, last summer.
Kennedy, who is the ex-wife of New York Gov. Andrew Cuomo, was charged with driving while impaired after she was involved in an accident July 12, 2012, on Interstate 684 in Bedford, New York, not far from her home.
Kennedy was on the way to her gym when she allegedly struck a tractor-trailer and continued driving for several miles before her car became disabled.
According to a release from the New York State Police, they received "911 calls reporting a white vehicle operating in an erratic manner." Police in North Castle, New York, responded and found Kennedy, 53, behind the wheel of her damaged Lexus SUV.
"A subsequent investigation found Kennedy to be operating the motor vehicle while her ability was impaired by drugs," the release said.
Kennedy's lawyer, Gerald Lefcourt, said his client had passed field sobriety tests but told State Police on the scene that she may have mistakenly taken an Ambien pill.
Subsequent toxicology results showed Kennedy had ingested zolpidem, the sedative in the Ambien prescription drug brand.
In the motion to dismiss, Kennedy provided a detailed description of what happened that morning.
"I awoke at approximately 7 a.m., and began to prepare to leave my home for the gym and then on to my office for a meeting. As part of that routine, I grabbed what at the time I believed to be my bottle of Synthroid (a thyroid medication) from the counter, removed a pill, and ingested it. ... While I remember getting onto 684, I have no further memory until a police officer knocked on my window as I was stopped at the light in Armonk. This was very disturbing to me, as I did not know why I had blacked out."
Lefcourt wrote in the motion, "It is inconceivable that any rational human being would knowingly and voluntarily ingest a sleeping pill before going to the gym to exercise. Not surprisingly, those who know her best are completely shocked by the allegations in this case and find them absolutely incredulous. ... A criminal conviction for Ms. Kennedy, after her years of extraordinary (public) service simply is unwarranted."
Neither Kennedy nor the driver of the truck were injured in the accident.
The prosecution has until March 26 to respond to the motion.