QUINCY - Washington State Patrol investigators suspect human error caused a March 12 school bus crash that injured several students near Quincy.

"We won't be able to say 100 percent for sure what caused the crash until we're totally done," Washington State Patrol (WSP) Detective Sergeant Jerry Cooper said Friday. "We look at human, vehicle and environmental causes. There's nothing with the vehicle or the environment that's popping out, and I don't anticipate it either as we go through the investigation."

Cooper, who leads the Major Accident Investigation Team, said interviews with bus driver Donna Eaton, 59, Quincy, matched previous witness testimony that noted there were no obstructions on the highway - such as a vehicle pulling from the shoulder or an animal crossing the road - and weather conditions were ideal at the time of the crash.

Speed was not a factor, as witnesses confirmed Eaton was travelling at just under the limit at the time of the crash, and an April 17 WSP interview with Eaton led investigators to rule out impairment or cell phone use as possible causes.

Cooper said he is unable to release details of the interview until the investigation concludes, which he estimated could take another 60 days.

"We're working on other aspects of this investigation and 17 others that we have going, but as far as the field work is concerned, we're wrapping it up," he said; adding the time line could change if the team of three WSP detectives is called upon to investigate new cases.

Eaton was placed on paid administrative leave following the crash, according to Quincy School District Superintendent Burton Dickerson, who said last week the driver will remain off duty until the WSP presents their case findings to the district.

Dickerson was unable to comment on what disciplinary action, if any, will possibly be brought against Eaton if human error is deemed the official cause of the crash. She has reportedly been with the Quincy School District for more than 20 years.

Cooper said a questionnaire is being sent out Monday to students who were on the bus when the crash occurred.

"One of the things we typically ask of any bus crash, whether it's a school bus or a tour bus, we try to get a read on where kids were sitting, who was sitting next to them and whether they saw or heard anything," he said. "It's kind of a formality to see if any new information comes to light."

Along with the driver there were 39 students on board at the time of the accident, ranging in age from kindergarten to 16 years old. All were injured to some degree, according to officials.

Dickerson said he could not comment on whether all of the students have fully recovered from their injuries, but he did say the district is "seeing more of a return to normal" in the months since the crash occurred.

The bus was travelling north on state Route 281 at about 8:20 a.m. March 12 when it left the road to the right a few miles south of Quincy, according to the Washington State Patrol. Eaton reportedly over-corrected and lost control of the bus, which rolled off the highway onto its right side, striking the ditch and coming to rest on its right side.