In the video, the 37-year-old argues with the trooper while he attempts to question her husband, Hollywood agent Jim Toth, after a traffic stop in Atlanta in the pre-dawn hours of April 19.
Toth pleaded guilty to a misdemeanor charge of drunken driving, Graham said. He was fined $600 and ordered to perform 40 hours of community service and participate in a program for driving under the influence offenders.
That is a "standard sentence for a first-time offender," Graham said.
In the dash-cam video, Trooper First Class J. Pyland tells Witherspoon to stay in the couple's vehicle no fewer than five times. Witherspoon is equally determined to get out and engage him, even at one point feigning to be pregnant and saying she needed to use the bathroom.
The video shows the situation quickly escalating.
When Witherspoon approaches and continues to try to intervene, the trooper starts placing her under arrest.
"You better not arrest me! Are you kidding me?" she asks.
"Nope," he responds.
She protests again, "I'm an American citizen!" The trooper leans toward her and says, "I told you to get in that car and stay in there didn't I?"
The petite Witherspoon turns to yell at the trooper as he's handcuffing her, and he warns her against resisting arrest.
"This is harassment!" she says. "You're harassing me as an American citizen! I have done nothing against the law!"
Witherspoon's husband mostly observes the exchange but tries to calm her after the trooper's warning. "Reese, can you please?" Toth asks.
While Witherspoon sits handcuffed in the police car, the trooper returns to view and tells Toth, "I tried."
Toth says "I'm sorry," and the trooper adds, "I absolutely 100 per cent tried."
Witherspoon, the star of hit movies such as "Walk The Line," "Legally Blonde," "Sweet Home Alabama" and "Election," said during her interview Thursday that "there are so many lessons learned."
"When a police officer tells you to stay in the car, you stay in the car," she said. "I learned that for sure. I learned a lot."
-AP