The probe's findings so far were sent Friday to Island County Prosecutor Greg Banks for review. Detectives are making no recommendation on whether charges are warranted, patrol spokesman Bob Calkins said.
That shouldn't be interpreted as a signal that detectives are recommending against charges, he added.
Reardon previously has denied any wrongdoing and described himself as the victim of an "appalling charade."
"We haven't done anything wrong," he said during a press conference Nov. 3. "We have checks and balances" in Snohomish County.
Reardon and his attorney, John Wolfe of Seattle, didn't immediately return phone calls Friday.
The patrol was asked to investigate Reardon by Snohomish County Prosecutor Mark Roe. Island County's prosecutor agreed to review the results to avoid any conflict of interest. Banks was away from the office Friday. Staff said he had yet to review the patrol's investigative report.
Until that happens, it is unclear whether the investigation is complete, Calkins said. He declined to describe what investigators learned or detail the specific allegations that were examined by detectives.
Calkins stuck Friday to what the patrol already has confirmed: The Reardon investigation has focused on allegations of official misconduct involving use of public funds.
"We are confirming that so far Mr. Reardon has chosen not to speak with us," but the offer to chat with detectives remains, Calkins said.
Word of the investigation surfaced in the final days of the general election contest that saw Reardon win a third term against state Rep. Mike Hope, R-Lake Stevens. Reardon claimed he was the victim of a political smear and suggested that Hope was behind the criminal investigation.
Instead, records show the investigation began in mid-October when Tami Dutton, a county social worker who has known Reardon since high school, alleged the executive for years had been using public money for county business trips that were opportunities for them to rendezvous for hotel room trysts.
Dutton took her story to County Councilman Dave Somers, who alerted prosecutors. She was granted whistleblower protection, meaning she likely won't face discipline. Dutton's supervisor said there is no evidence that she misused county resources.
Dutton in March told The Herald that she reported the alleged misconduct because she believed her family was being stalked.
"I've taken responsibility for my own actions," she said earlier.
Reardon's phone bills show him on his government cellphone with Dutton for more than 11 hours between January and July. More than 80 percent of that time was on weekdays during regular business hours, excluding the noon hour. Some of the calls lasted more than an hour.
Early in their investigation, patrol detectives obtained Reardon's appointment calendar, thousands of his emails and government cellphone bills detailing roughly 10,000 calls and texts.
An analysis by The Herald found Reardon using his county phone to call and exchange text messages hundreds of times with key campaign staff and contractors.
Reardon also spent the equivalent of a work week dialing up donors seeking campaign dollars. During those times, his schedule showed him holding a series of "in-office" meetings with staff.
It is against state law to use public resources for political campaigns.
The state Public Disclosure Commission says it has been awaiting the results of the State Patrol investigation before initiating a review of Reardon's campaign activity.
Meanwhile, Reardon supporters have been pointing to results of a glowing annual audit of the county's books as evidence that nothing is amiss. State auditors have made clear, however, that the examination was separate from one that they were asked to conduct for patrol detectives, which focused on purchases and travel-related expenses.
The county's travel records were described as being incomplete and in disarray. State Auditor Brian Sonntag stood by that description, despite a letter from the executive's office challenging the characterization.
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