An aide who was with the former four-term South Dakota governor at the time of the crash testified that he believed Janklow slowed before the accident.
Highway Patrol Sgt. Gene Barthel, an accident reconstructionist, used a large map to show jurors the location of roads, stop signs, Janklow's Cadillac, the motorcycle and the body of its rider, Randy Scott.
He said he based his estimate of Janklow's speed on a scientific formula that takes into account the vehicles' weights, paths and positions.
Janklow, 64, is charged with second-degree manslaughter, speeding, running a stop sign and reckless driving in the Aug. 16 collision that killed Scott, 55, of Hardwick, Minn.
Defense lawyer Ed Evans acknowledges that Janklow was speeding but said the congressman did not see the stop sign because he had a diabetic reaction that caused him to become disoriented.
Chris Braendlin, an aide who was in the car with Janklow, testified Wednesday that Janklow didn't have anything to eat that day but seemed fine on the trip. He said the car's speed changed.
"I remember slowing down but I don't remember where," Braendlin said.
He also said he remembered seeing a motorcycle.
"This is one event. And I can't recall what order," Braendlin said. "It was motorcycle, flash, spinning."
Barthel said Scott was traveling at 59 mph on an east-west road that did not have a stop sign. Neither driver took any evasive action, he said.
The motorcycle hit the back of Janklow's car and Scott's body slammed into the car's trunk before landing in a field, the officer testified. Janklow's car spun around several times before stopping, he said.
The trial threatens to derail the career of a colossal figure in South Dakota politics. Janklow, a Republican, is a former state attorney general who served 16 years as governor during two stints before being elected to the state's only House seat last year.
On Tuesday, a friend who had been riding another motorcycle ahead of Scott wept on the witness stand. "I kneeled down to see if he had a pulse and he didn't," Terry Johnson said.
The jury also saw a videotape taken by the Highway Patrol just hours after the accident in which Janklow was told Scott's name and birth date. Janklow said something about Scott not even being 60 years old, then asked about his family, paused, sighed and said: "Jesus."
The videotape was taken when Trooper Jeff Lanning drove Janklow to a hospital for a blood-alcohol test. During the ride, Janklow sounded coherent most of the time and was able to recall things, though he did not remember details of the accident.
Janklow told the trooper several times he swerved and sped through the intersection to avoid hitting another vehicle.
"It was a white car," he said. "I thought that's who hit me."
But on the way back to the accident site, Janklow seemed to question whether he had seen the vehicle — "Maybe I'm dreaming."
If convicted of manslaughter, the maximum punishment is 10 years in prison. It would also prompt the House ethics committee to investigate.
The committee's rules say representatives who plead guilty or are convicted of a crime that carries two or more years in prison should refrain from voting or taking part in committee meetings in the chamber until his or her record is cleared or until re-elected.