Witnesses saw a car slowly drift into the opposite lane of traffic.
A driver following behind Jennett said it look like she was speeding, but wasn't driving recklessly.
"I kept thinking there's time to pull back over, there's time for the car to get back over, and it just kept coming toward the yellow line," Biggers said.
Jennett's attorney says there's no way to tell what caused the crash on that clear summer day.
It could have been the sun in her eyes, or maybe something else.
"You can't really rule out there being a problem with her car with the steering?" defense attorney Paul Stockler asked State Trooper Howard Peterson.
"That's correct," Peterson answered.
"There's lots of possible causes for this accident we just don't know what caused it, correct?" Stockler continued.
Jennett wasn't drunk. A test showed Jennett's blood alcohol level was well below the legal limit. Investigators found an anti-anxiety drug in her urine, but prosecutors didn't bring that up in the case.
"How long or how many months did you continue to investigate this collision?" prosecuting attorney Clint Campion asked Peterson.
"Up until probably months ago," he answered.
The man driving the pick-up, Jeffrey McClure, was pinned to his steering wheel. He died at the scene.
"After the accident I went up to it and pulled the cab off and tried to give as best assistance as I could," said Lee Wasson, who saw the accident.
Jennett's passenger, Riley McVitty, made it through the night, but was pulled off life support a few days after the crash.
"It's hard to look at your son. In 23 years he had never had a broken bone or a stitch so I had never seen him in that condition before," his father, William McVitty Jr. said.
Even more than a year and a half later, there are lots of people watching, still trying to figure out why Jennett crossed the line.
Jennett hasn't said whether she plans to testify. The trial will wrap up next week.
The prescription anti-anxiety drug found in her system is known to cause drowsiness, but the judge threw that argument out early on in the case.
Contact Ashton Goodell at firstname.lastname@example.org