The trooper was deeply skeptical. He figured out how to subpoena Mr. Shaw’s phone records. Six months later, with help from a state public safety investigator, they got the records and their proof: Mr. Shaw and his girlfriend had sent 11 text messages to each other in the 30 minutes before the crash, the last one at 6:47 a.m., a minute before Mr. Shaw called 911. Investigators concluded he sent that last text when he crossed the yellow line.

Still, county prosecutors thought they were unable to charge Mr. Shaw with something other than “left of center.” For instance, if they wanted to prove Mr. Shaw guilty of negligent homicide, a misdemeanor, they would need to show he knew of the dangers or should have known of the dangers of texting while driving.

Mr. Shaw, who had retained a lawyer, would not discuss the issue with law enforcement or prosecutors.

Then Terryl Warner, a victim’s advocate in the county where the accident occurred, got involved.

Ms. Warner had a personal interest in the case because she knew the family of one of the scientists.

In July 2007, Ms. Warner, convinced by the trooper’s evidence, wrote to prosecutors arguing for a vehicular manslaughter charge. She said the dangers of texting and driving were broadly known, therefore Mr. Shaw should have known better.

Mr. Shaw had just started a Mormon mission in Canada when he was called home to face charges of negligent homicide. The trial was set for early 2009.

Then, just before Thanksgiving in 2008, at a hearing, Mr. Shaw looked at the families of the two dead scientists and decided he could no longer keep dismissing the phone records that showed he was texting, even though his lawyers advised him to remain quiet. “It hit me that I was being selfish dragging this on,” he said. “I decided I’ve got to do whatever it takes to make this come to an end. If there was anything I could do  spend a year in jail, two years in jail, whatever  I’d do it.”