LARGO — It was Super Bowl Sunday. Brett Dowd and his fiancee, Brittany Byrne, had just arrived at the Twin Lakes apartment complex in Palm Harbor for a cookout with friends. Their 2-year-old son was in the back seat.

But as Byrne, who was driving, pulled into a guest parking spot, a black Nissan headed toward them. Both cars came to a halt, avoiding a crash.

Dowd and the other driver, Sheila Langlais, lowered their windows and exchanged profanity-laced words. When he insulted Langlais with another obscenity, Langlais, a Pinellas sheriff's deputy at the time, grabbed her gun and pointed it at Dowd with both her hands, said Pinellas-Pasco Assistant State Attorney Robert Bruce. She warned them: "I know how to use it."

Then she sped off.

The Feb. 7 confrontation resulted in Langlais' arrest in March and her resignation from the Sheriff's Office. It was the third time she had resigned from a law enforcement agency under pressure. Her trial for two felony counts of aggravated assault began Thursday. If convicted, Langlais, 47, faces up to 10 years in prison.

But defense attorney Donnie Scruggs told the six-member jury a different story. When Langlais was driving on U.S. 19 toward the apartment complex to visit a friend, Byrne had already cut her off twice on the highway.

"She didn't realize the same vehicle that just cut her off twice was going to the same destination," Scruggs said.

Byrne cut her off again, this time in the parking lot. Yes, Scruggs said, Langlais did exchange words with Dowd.

But as a law enforcement officer, Langlais is trained to know "when situations are about to get out of hand," Scruggs said. So she retrieved her gun.

"She's had many interactions on a daily, weekly, or monthly basis when the situation is just not right," he added. This was one of them.

Seconds later after showing her Glock pistol, she drove off, Scruggs said. She never got out of her car, he added, or said she was going to shoot. Prosecutors also don't have evidence to support the second count of aggravated assault because the entire argument was between Dowd and Langlais, he said. Byrne, Scruggs explained, was not involved.

Bruce, the prosecutor, also said Langlais lied to detectives during their initial investigation. After Dowd called 911 and gave them a partial tag of the Nissan, deputies found the car elsewhere in the complex and located Langlais, who was visiting another deputy.

At first, Langlais denied carrying a gun. She later admitted she was armed. Deputies found the Glock on a shelf in the apartment of the deputy Langlais was visiting. She also changed out of her pink shirt after the confrontation, Bruce said.

Langlais resigned from the Sheriff's Office during the State Attorney's Office investigation and was arrested in March.

Langlais had a rocky beginning and end to her law enforcement career.

She was hired by the Tarpon Springs Police Department in 2000, but resigned a year later while under investigation for developing a romantic relationship with a sergeant, records show. In 2001, she started working at the Pinellas Park Police Department, where she failed to end a pursuit as instructed by a supervisor. She resigned in November 2005.

The Pinellas County Sheriff's Office hired Langlais as a criminal justice specialist, a nonsworn position, in March 2013. She became a deputy that summer when her supervisors offered positive feedback of her work.

Testimony will resume today.

Contact Laura C. Morel at lmorel@tampabay.com. Follow @lauracmorel.