Kerry Kennedy will plead not guilty today to driving under the influence of drugs after a collision with a tractor-trailer last week, ABC News has learned.
Authorities say Kennedy, a human rights activist and the daughter of the late Sen. Robert F. Kennedy, was seen driving erratically in Westchester, N.Y., Friday when she collided with the truck. She allegedly continued driving and was later found slumped over the wheel of her car, reportedly unable to remember what had happened.
In the wake of the accident, Kennedy, 52, said to police she might have taken the prescription drug Ambien, sources said. Kennedy was arrested and charged with driving while impaired.
"We know in my family that this is out of character for Kerry, and we're worried about this as anybody would be when a loved one is in a car accident," her cousin and former Rhode Island congressman Patrick Kennedy said.
He made similar headlines in 2006 when he was involved in an accident in Washington, D.C. He was arrested for driving while intoxicated, and he had taken a sedative before getting behind the wheel.
He says the family is unsure what happened with his cousin last week.
"[The 2006 accident] was a wake-up call for me in many respects. These are medications that are very powerful, and if it was a medication like Ambien, then it's something that we all need to be aware of," he told ABC News.
Patrick Kennedy said that unlike his own struggle with depression and mental illness, his cousin Kerry has no history of problems with prescription drugs.
"Kerry is certainly is somebody who, I think, is a resilient person," he said. "I know she'll be moving forward."
She is New York Gov. Andrew Cuomo's ex-wife.
Rocco Scuitello, the driver of the truck that Kennedy hit, told the New York Post today, "My first impression was that she was really, really drunk, half asleep or very, very intoxicated. She's very lucky she didn't kill somebody."
"When she hit me, my left tire tore up her passenger-side door, and the lug nuts on my truck tore up her tire, just shredded through it and peeled the tire right off," Scuitello said.
"She woke up a little bit, not a lot, not the way you'd wake up if you'd just hit a 6,000-pound truck. The only thing she wanted to do then was get away, because she floored it and took off."
Patrick Kennedy said he was with his cousin at a wedding last week and that the accusations are completely out of character.
Kerry Kennedy's family said in a statement released to ABC News that there were no drugs involved.
"Kerry Kennedy voluntarily took breathalyzer, blood and urine tests -- all of which showed no drugs or alcohol whatsoever in her system. The charges were filed before the test results were available," the Kennedy family said in a statement released Friday.
The results of Kennedy's toxicology tests are pending.