Snohomish County Executive Aaron Reardon won't be charged with misuse of public funds, but still faces a noncriminal investigation into whether he used county cellphones and offices during his re-election campaign.

The Island County Prosecutor's Office, citing insufficient evidence, said Wednesday it will not file charges against Reardon after a State Patrol investigation into county employee Tamara Dutton's claims she had a long-running affair with Reardon and that he spent at least $1,500 of taxpayer money on her when she accompanied him on official trips.

Reardon, a Democrat who denied any wrongdoing, claimed it was a politically motivated attack.

He refused to talk to the State Patrol as part of the investigation, which was his right, Island County Prosecutor Greg Banks said in a news release Wednesday.

"Our decision not to prosecute Mr. Reardon is simply that — a decision not to bring a criminal case. Nothing more concerning Mr. Reardon's official or unofficial conduct should be read into my conclusion that I had insufficient evidence to charge him with a crime. I did not consider any other aspects of his conduct in making my decision," Banks wrote.

The Island County Prosecutor's Office had been reviewing the findings of a State Patrol investigation, launched at the request of the Snohomish County Prosecutor's Office.

Reardon did not return phone calls Wednesday, but his attorney, John Wolfe, issued a statement praising the prosecutor's decision as a "a triumph for the rule of law over what appears to have been a thinly disguised and improper effort by Mr. Reardon's political adversaries to undermine the electoral will of the people."

Snohomish County Councilman Dave Somers — who in February sponsored a resolution asking Reardon to take a leave of absence — said the decision brings resolution. "I really am relieved that we're through the investigation. It's been a long difficult six months; having it come to a close is a relief."

Somers had called for the investigation after Dutton reported her allegations to him.

"It's a relief?" Dutton said Wednesday. "Is that all he can say?"

Dutton said she was upset because she was told her identity would be protected. "I would never go forward again," she said. "I'm ... mad, and it has nothing to do with Aaron not being charged. It's the way I've been treated. It's been a goddamn nightmare, and I would not suggest anyone else do it."

Dutton said she does not believe the State Patrol took her seriously. She said that rather than give her the results of its investigation as a key witness in the case, she said she was told to get the information from the news media.

Public Disclosure Commission (PDC) spokeswoman Lori Anderson said Reardon now will be investigated by the PDC for allegedly using county cellphones and offices during his re-election campaign, an inquiry that was put on hold in February while the State Patrol looked into the other allegations.

Somers said the PDC has not contacted the county for documents but that he is aware there were issues raised during the State Patrol investigation about the use of county property during Reardon's campaign.

Somers said that to him, the campaign issue and the allegations that Reardon misused county funds "were always separate issues."

The State Patrol did not make a recommendation about whether charges should be filed when it turned over its findings to Island County in early May.

Banks said charges he considered were misappropriation and falsification of accounts by a public officer, theft and official misconduct.

In each case, there was not enough evidence to charge Reardon, Banks said.

He wrote that "even the complaining witness had doubts about who was paying for Mr. Reardon's travel, whether Mr. Reardon paid for meals and lodging using a county or personal credit card.

"She (Dutton) did not know whether Mr. Reardon reimbursed the county for personal expenses that were put on a county credit card," Banks wrote.

Reardon's extensive national and international travel often was paid for by organizations other than Snohomish County, such as nongovernmental and political organizations.

"The county's documentation of Mr. Reardon's travel reimbursement for official county travel did not substantiate Ms. Dutton's suspicions about misuse of county funds," Banks wrote.

The State Auditor was asked to review the Snohomish County Executive Office's expense-reimbursement practices during its annual audit and concluded there were adequate controls to assure the public that their money was being spent only on official business, Banks said.

Other trips that were investigated occurred so far in the past that the statute of limitations for filing had expired and the age "made it difficult to find credible witnesses with memories of the events in question, even if wrongdoing had occurred," Banks wrote.

Reardon has not denied an affair with Dutton, whom he has known since high school.

Dutton has produced records that back up her claims, and a second woman has said she also had a sexual relationship with Reardon, who is married. Records released as part of the investigation showed the executive made personal and campaign calls on his taxpayer-paid phone and raised money for his campaign while his official calendar said he was in staff meetings.

With criminal charges off the table, Reardon's political future remains in question.

Republican public-affairs consultant Chris Vance said he thinks Reardon's career can be salvaged.

"At one point, Aaron Reardon was viewed as this rising star who was going to be running for governor. Obviously this is a huge hit for him," he said, but added that by basically ignoring the allegations, refusing to step down or acknowledge any misconduct, Reardon may have preserved his career.

It's the same strategy Bill Clinton used, Vance said. Clinton is a political role model of Reardon's.

"Aaron Reardon, same thing, there's very little doubt that he engaged in very embarrassing conduct. ... But now he can look people in the eye and say, 'I didn't break the law.' "

Times staff reporter Emily Heffter contributed to this report.

Nancy Bartley: 206-464-8522 or nbartley@seattletimes.com. On Twitter @BartleyNews.