As security staffers prepared to pull the fire alarm, a Seattle Police Department officer arrived on the scene. Although accounts differ on the precise details of what happened next, library staffers were quickly told to call off the evacuation, and the responding police officer, along with a man in street clothes (identified after the fact, according to the police report, as U.S. Army Sgt. Maj. Mike Merzke) and two other plainclothes officers left the building, carrying the mysterious devices with them.

Merzke, who works at the U.S. Army's Special Operations Command (USASOC) in Fort Bragg, NC, did not return a call to his direct line seeking comment. According to USASOC public affairs director Robert Bockholt, the exercise was part of a larger series of "realistic military training" exercises that took place in locations across the city between April 8 and April 22. "Seattle, like other cities, provide an excellent training area for the challenges of an urban environment and afford our Soldiers the opportunity to refine our techniques needed for overseas operational missions," Lt. Col. Bockholt said in an email. "The Seattle Police Department approved and coordinated with USASOC from October of 2017 through April of 2018, including two in-person meetings in Seattle prior to training commencement."

According to Bockholt, "The training and evaluation device[s]"—the books—"included an embedded recorder [and] allowed military training staff the ability to evaluate the students['] training." Bockholt did not provide additional information about the other training exercises it conducted in Seattle in April.

Library spokeswoman Andra Addison says the library was not informed in advance about the exercise.

In an email to library staffers a week after the near-evacuation, city librarian Marcellus Turner wrote that he had talked to SPD at length about "why we aren't a good place to hold" military exercises, and that "Chief [Carmen] Best and her staff at the police department ...apologized immediately" for the incident and assured him that "[t]he Seattle Public Library (and our neighborhood libraries) will not be an exercise site again."

"I have been assured that the exercise itself never placed the library or any of our staff or public in danger or harm of any sort and the devices that were found had no ability to harm or physically disrupt our space or use of the building," Turner continued. "The exercise was a constitutionally-protected and non-criminal exercise meaning having a conversation in a public space and possessing no weapons in the course of the exercise was legal. The exercise itself was described as a meeting between several people in a public space and the device that was found was a recorder which was being used to record the discussion between these people. In truth, an exercise of the agency / agents, not the Library."

The Seattle Police Department declined to comment on its role in the incident. Bockholt said that the Army's policy "with regards to informing local governments when conducting these kind of exercises in public buildings is to coordinate and follow local law enforcement guidance. In this case, Seattle Police Department evaluated the training and determined their supervision of the training was sufficient."

Library spokeswoman Addison says library staffers "did a great job of responding calmly and appropriately" when they found the devices.