Authorities are investigating an intriguing mystery behind the Sept. 5 plane crash in western San Juan County that killed four people, seeking answers as to why the small plane had gone so far off its intended course and exploring possible links to a methamphetamine bust.

The National Transportation Safety Board is expediting its examination of debris recovered from the crash site because of the suspicious circumstances regarding the flight, an investigator said. That examination is being conducted at the NTSB’s Greeley facility.

The flight from Barstow, California, with four California residents aboard, was reportedly en route to Amarillo, Texas. But after refueling at Flagstaff, Arizona, it veered far to the north of its purported flight path.

And among those on board was Steven Wilkinson, 59, of Newberry Springs, California, who was arrested Sept. 1 by the San Bernardino Sheriff’s Department in connection with the sale of methamphetamine, being in possession of methamphetamine while armed and being a felon in possession of a firearm.

Wilkinson’s previous criminal history includes pleading guilty to possessing an illegal substance with intent to sell in 2008. He also pleaded guilty to possessing illegal drugs in 2003, according to San Bernardino County Court records.

Wilkinson’s latest arrest was part of a large law-enforcement operation conducted Aug. 31 and Sept. 1. The operation also included the seizure of about 11,000 marijuana plants and resulted in charges against 34 people in the Barstow area.

Jodi Miller, spokeswoman for the San Bernardino Sheriff’s Department, said Wilkinson posted $50,000 bail Sept. 2. She had no information on the conditions of the bail, including whether or not he was barred from leaving California.

The twin-engine Cessna was owned and piloted by Wilkinson’s father-in law, Harold Joseph Raggio, 72, of Big Bear, California. Also killed in the crash (along with Wilkinson and Raggio) were passengers Rosalinda Leslie, 57, of Hesperia, California, and Michael Lyle Riley, 59, of Barstow.

Law-enforcement officials, including the FBI, refused to discuss the case.

Ron Hamm Jr., operator of Daggett Aviation at the Barstow-Daggett Airport, said he knew three of the people on the plane but did not know Wilkinson.

“I didn’t know the individual. But I knew of him. He was a shady character with a lot of bad history,” Hamm said.

Hamm told the Standard that there is rampant speculation in Barstow as to why Wilkinson was aboard the flight.

“Rumors at the local bars” are that Wilkinson was “either going out there to get money to make a big deal or to help him with his current ‘lawyer stuff’ because of that bust,” Hamm said. “Or he was going to get dropped off and not come back.

Another acquaintance described Wilkinson as someone who “ruled that desert out there with an iron fist.”

Hamm said that Raggio’s wife told him that “he was flying out to have dinner with friends in Amarillo and then coming right back.”

The flight left Barstow at about 7 a.m. It crashed in San Juan County at about 2:08 p.m. Sept. 5, according to the NTSB investigation.

Hamm said he was the one who started the search for the missing plane, flying as far as Flagstaff himself, where he learned the plane had refueled.

The NTSB issued a preliminary report on Sept. 17 saying the flight encountered “instrument meteorological conditions” over western Colorado, but neither of the two pilots aboard was qualified to fly in such bad weather.

The NTSB report indicates the twin-engine Cessna 310H “impacted mountainous terrain at an elevation of about 11,500 feet.”

Weather was partly cloudy in Silverton that day, but there were some rain squalls, and a thunderstorm was reported in the area.

The wreckage was located the next day near the head of Cascade Creek at Grizzly Peak, about nine miles west of Silverton.

Sheriff Bruce Conrad described a path of destruction, with the plane pulverized by the impact.

The preliminary NTSB report points out that the two pilots aboard were not rated to fly a twin-engine plane, and they were not operating on a flight plan.

Additionally, the pilot was not using “flight-following services by air traffic control,” the NTSB reported.

Herald Staff Writer Mary Shinn contributed to this report.