Umatilla County District Attorney Dan Primus said the case is "very complex" and he has not convened a grand jury.
"I don't know if I would say we're close (to a decision)," Primus said this week. "We're in the process of evaluating as well as we've been working with other federal agencies and collaborating with them in trying to potentially make a joint decision on how to move forward - if we move forward."
Nine people died and almost 40 were injured Dec. 30 when a bus carrying tourists on an icy highway smashed through a guardrail east of Pendleton and rolled down a hill.
In January, the U.S. government banned Mi Joo Tour & Travel and driver Haeng Kyu "James" Hwang - both based in Vancouver, British Columbia - from operating commercial vehicles on American roads. Witnesses said the bus was traveling too fast for the wintry conditions, according to an order issued by the Transportation Department's Federal Motor Carrier Safety Administration. The agency also said Hwang had worked 92 hours in an eight-day stretch, surpassing the federal limit of 70.
Attorneys for Mi Joo Tour & Travel have said black ice - not driver fatigue or excessive speed - caused the crash.
Primus said his focus is on the actions of the driver, not the tour company. He said he has not been in contact with Canadian authorities.
Oregon State Police detectives have completed their investigation and submitted the findings to Primus. Neither Primus nor police would release the report this week.
Aside from the criminal investigation, the state's deadliest crash since 1971 has brought a flurry of lawsuits from the injured and relatives of the dead.
The crash happened while Mi Joo Tour & Travel was operating two 57-passenger buses on the final leg of a nine-day journey through the West.
The bus driven by Hwang plunged through the guardrail on a foggy morning just before an infamous downgrade known as Cabbage Hill. A snowplow had applied sand to the road a few hours before the crash and was behind the bus making another run when the tragedy occurred.