Ellis, who currently serves as chief deputy state treasurer, eliminated Walker in the June 24 primary to win the Republican nomination.
Ellis filed a complaint in late May with Lt. Gov. Gary Herbert's office, alleging that Walker told him in March he could keep his job, and get a raise - from $104,000 to $160,000 - if he'd withdraw from the race.
A sworn affidavit from Ellis alluded to an unnamed influential lawmaker who told Walker he could make the pay hike happen.
"The investigation is progressing and we're going to do it as thoroughly, fairly and quickly as we possibly can," Davis County Attorney Troy Rawlings said Thursday.
"We realize there's a public need for the results so we're working diligently toward that goal," he said. "But we're not going to rush it because it has to be fair and complete."
Rawlings, a Republican, and Weber County Attorney Mark DeCaria, a Democrat, were appointed by the state Attorney General's Office to conduct the probe.
A parallel House Ethics investigation screeched to a halt earlier this month, just hours after Walker, a two-term House member from Sandy, resigned his legislative seat.
The two county attorneys declined to provide details of the investigation, including possible witnesses. But a list of subpoenas issued by the ethics committee and obtained by The Salt Lake Tribune through a records request provides a likely pool of prospective witnesses.
The list includes Ellis, Zions Bank executive Carl Empey, bank employee Mickey Taylor, Rep. Paul Ray, R-Clearfield, and Lt. Gov.'s Deputy Chief of Staff Michael Cragun.
In a June 26 letter to the committee, attorneys for the five House members who filed the ethics complaint submitted their recommended witness list. In addition to Walker and Ellis, the roster included Empey, Lt. Gov. Gary Herbert, state GOP Party Chairman Stan Lockhart, GOP consultant David Hansen and Zions Bank employees Shane Giddings and Mickey Taylor.
