EVERETT — Washington State Patrol detectives spoke to nearly two dozen people and reviewed thousands of records before concluding that only the spending involved with a single trip in 2010 was relevant to allegations that Snohomish County Executive Aaron Reardon used taxpayer money to further an affair, records released Tuesday show.

Island County Prosecutor Greg Banks earlier this month announced that he’d been presented insufficient evidence to charge Reardon with criminal official misconduct.

The full patrol investigation includes more than 13,000 pages of documents, which are being released piecemeal. On Tuesday, more than 90 pages from the patrol investigation were released under public records laws.

The documents describe interviews with 23 people connected to the case, including past and present members of Reardon’s staff, employees responsible for running the county’s computer systems, other politicians and a Boeing Co. representative.

Only Reardon and a junior member of his staff, analyst Kevin Hulten, declined detectives’ requests to arrange interviews, the reports say.

Summaries of the detectives’ findings make clear that only a trip Reardon took to Chicago in September 2010 fell within the time frame for the investigation.

Investigators “were looking for any evidence that Executive Reardon used county credit cards or county funds for personal purchases,” the reports said.

They found just $6 that couldn’t be accounted for — and it likely was cab fare charged to the county for Tami Dutton, the woman who said she’d engaged in a long-running affair with Reardon, the reports said.

Along the way, though, investigators were told there were reasons to question how Reardon came to own a house in Southern California and allegations about electronic county records being improperly destroyed.

The reports released Tuesday don’t address what investigation was done on those issues.

The detectives did note evidence that Reardon and Dutton shared long phone calls, but they appeared to leave it up to state campaign investigators to determine whether those same phone bills show Reardon campaigning on the public dime. When detectives asked, Reardon’s staff said they had not seen him using public resources for his campaign.

Patrol investigators focused their efforts on whether Reardon committed official misconduct. That is a gross misdemeanor that applies to public servants who attempt to benefit by committing an unauthorized act or by refraining from carrying out a legal duty. They also explored information relevant to charges of misappropriation and falsification of accounts by a public officer.

The investigation started in October, after Dutton, a county human services employee, went to the County Council to report going on county business trips with Reardon that she believed he paid for using county credit cards.

“Dutton claimed that during the trips she paid for her airfare and Executive Reardon paid for the hotel, their food and transportation,” according to investigative notes. “Dutton believed Executive Reardon paid for these costs with county credit cards.”

Dutton provided detectives with five photographs that she said were taken during the Chicago trip. The detectives’ reports don’t detail whether Reardon appears in any of the images.

Dutton told detectives she and Reardon had carried on an extramarital affair for six years, starting in 2005. The two have known each other since attending Mariner High School together in the 1980s.

Dutton told detectives Reardon attended one meeting during the Chicago trip but left after 90 minutes, claiming he had a headache.

Most costs for the trip were paid for by a national Democratic leadership group. Snohomish County paid $82.80 for two cab fares. During that trip, Reardon paid for his meals and did not put in for reimbursement or claim per diem.

There are two unexplained extra fares on the cab receipts totaling $6. Dutton told investigators the extra fares were for her.

Detectives reported they were provided paperwork from Reardon’s former executive assistant, Nancy Peinecke, detailing what happened when a hotel “intimacy kit” was charged to Reardon’s county credit card after a 2007 trip to Washington, D.C. Reardon paid the bill with his own money after a county staffer brought it to his attention, records show.

In announcing the decision not to file charges, prosecutor Banks made it clear that he wasn’t condoning Reardon’s conduct, just examining it in light of the law.

Reardon now is under investigation by the state Public Disclosure Commission focusing on whether he repeatedly violated state campaign laws.

A Herald analysis of campaign and office records shows Reardon spent 2011 making extensive use of taxpayer resources, including dialing for dollars on his government cellphone during periods when his schedule and emails show him arranging “in office” meetings with his campaign fundraising consultant.

Noah Haglund: 425-339-3465, nhaglund@ heraldnet.com.