What we know about the off-duty Alaska Airlines pilot accused of trying to shut off a plane's engines mid-flight

The off-duty pilot accused of trying to shut down the engines of an Alaska Airlines plane midflight on Sunday said he was having a nervous breakdown and told the flight crew he needed to be subdued, according to a federal complaint.

Alaska Airlines pilot Joseph D. Emerson, 44, has been charged in federal court with interfering with a flight crew, the US Attorney's Office for the District of Oregon announced Tuesday. That charge comes on the heels of dozens of state charges in Oregon, including 83 felony counts of attempted murder, 83 counts of reckless endangerment and one count of endangering an aircraft, booking records show.

Emerson attempted to cut fuel to the plane's engines while the flight was en route from Washington state to San Francisco on Sunday, according to authorities. But it was the quick action of the aircraft's captain and first officer that kept the engines from failing completely, the airline said.

Emerson was subdued by members of the flight crew but then attempted to grab the handle of an emergency exit during the flight's descent, according to a release from the US attorney's office.

The flight was forced to divert to Portland, Oregon, where the suspect was taken into custody by Port of Portland police, the agency said in a statement.

While in custody, Emerson told a police officer he became depressed about six months ago, according to an affidavit authored by an FBI agent and included alongside the federal complaint. Emerson denied taking any medications, the affidavit says, but he did discuss psychedelic mushrooms with the responding officer.

"The officer and Emerson talked about the use of psychedelic mushrooms and Emerson said it was his first-time taking mushrooms," the affidavit says.

Asked specifically if Emerson told officers he had been under the influence of mushrooms at the time of the incident, a spokesperson for the US Attorney's Office in Oregon told CNN that remains part of their ongoing investigation.

While in custody, Emerson said he was "admitting to what I did," per the affidavit. "I'm not fighting any charges you want to bring against me, guys," he said.

Emerson is being held without bail at the Multnomah County Jail and is expected in court on the state charges Tuesday afternoon. Online records do not list an attorney for Emerson, and CNN has been working to determine if he has legal representation in both state and federal court.

Authorities do not believe the incident was an act of terrorism or ideologically motivated violence, a law enforcement source familiar with the investigation told CNN. Investigators believe it may have been the result of a mental health episode, and authorities are preparing for court officials to order an assessment of the defendant's psychological state as part of court proceedings, the source said.

Here's what we know.

After taking off from Everett, Washington, on Sunday, Alaska Airlines Flight 2059 - operated by regional carrier Horizon Air - reported a "security threat related to an off-duty Alaska Airlines pilot, identified as Captain Joseph Emerson, who was traveling in the flight deck jump seat," the airline said in a statement.

Pilots will sometimes ride in a cockpit "jump seat" when traveling in their official capacity or commuting between airports.

While in the cockpit, Emerson had tried to shut down both of the Embraer 175's engines by pulling its fire extinguisher handles, the airline said.

"The fire suppression system consists of a T-handle for each engine; when pulled, a valve in the wing closes to shut off fuel to the engine," Alaska Airlines said in a statement to CNN. "After they are pulled, some residual fuel remains in the line."

The airline said the quick reaction of the crew to reset both handles helped restore the flow of fuel and prevented the engines from cutting out.

"Our crew responded without hesitation to a difficult and highly unusual situation, and we are incredibly proud and grateful for their skillful actions," the airline said in a statement.

Emerson initially engaged the pilots in small talk about the weather and the aircraft, the affidavit says. He then said, "I'm not OK," and one of the pilots turned around to see him reaching up and grabbing the red fire handles, the affidavit says.

One of the pilots grabbed Emerson's wrist while the other declared an inflight emergency, the affidavit says. One pilot said Emerson "initially resisted," and the two "wrestled" for about half a minute before Emerson agreed to leave the cockpit.

"I think he's subdued," one of the plane's pilots can be heard saying in air traffic control audio recorded by LiveATC.net. "Other than that, we want law enforcement as soon as we get on the ground and are parked."

After "peacefully walking to the back of the plane," the affidavit says Emerson told a flight attendant, "You need to cuff me right now or it's going to be bad."

The crew cuffed his wrists, but during the descent, Emerson "turned towards an emergency exit door and tried to grab the handle," and was stopped by a flight attendant, the affidavit says.

"Another flight attendant observed Emerson make statements such as, 'I messed everything up' and that 'he tried to kill everybody,'" the affidavit says. "Emerson was heard saying he had just put 84 peoples' lives at risk tonight including his own."

When the flight landed at Portland International Airport around 6:30 p.m., the suspect was taken into custody by Port of Portland police officers, the port said.

No injuries were reported on the flight, the FBI said.

All passengers were later able to fly to San Francisco with a new crew and aircraft, the airline said, noting it is "reaching out to each of them individually to discuss their experience and check-in on their well-being."

The FBI and the Port of Portland police are investigating the incident, authorities said.

The FBI's Portland field office confirmed its investigation in a statement Monday and assured travelers there is "no continuing threat related to this incident."

The Federal Aviation Administration also said it is supporting local law enforcement in the investigation.

The FAA said it has briefed other airlines on preliminary details of the incident and informed carriers the incident is not related to "current world events" - apparently referring to the war in the Middle East between Israel and Hamas.

Two passengers on the flight told CNN that the airline crew maintained a calm environment on the plane as the incident played out.

Aubrey Gavello, one of the passengers, said she didn't realize something was wrong until a flight attendant announced over the loudspeaker that the plane needed to land immediately.

"We didn't know where we were landing, and we didn't know what was wrong. But (the flight attendant) assured us we were safe," Gavello said on CNN's "Laura Coates Live" on Monday night.

Later, the pilot informed passengers through the loudspeaker that there had been a "disturbance in the cockpit," said Alex Wood, who was seated at the front of the plane. Wood said he was wearing headphones and slept through the incident.

"I was right by the cockpit, but nothing woke me up. Nothing was loud enough, nothing was rambunctious enough to wake me up," Wood said.

About five police officers boarded the plane after it landed and escorted the suspect off the aircraft, Gavello recalled. She noted he was calm and cooperative and had his hands secured by zip ties.

After Emerson was taken off the plane, a flight attendant announced on the loudspeaker that "he had a mental breakdown," Gavello told CNN affiliate KGO.

"Props to the Alaska crew for keeping everyone calm," Gavello told CNN.

"It was all handled super well," said Wood.

The pair said they didn't realize the gravity of the situation Monday, when they woke to news headlines about the suspect trying to shut down the plane engines.

"I'm honestly grateful that we didn't know anything when they rebooked us and got us on a second plane," Gavello said. "I don't know if I would have felt comfortable doing that if we had all the information."

Emerson's neighbor, Ed Yee, told CNN it was "very shocking" to hear of the suspect's alleged actions.

"He seems like a really nice guy. Nothing abnormal about him," Yee said.

Emerson had his most recent FAA medical examination last month, records show. He has a first-class medical certificate, the highest level of medical certificate awarded by the agency, which requires examinations every six months for pilots 40 and over.

Emerson has worked in aviation for at least two decades, according to information shared by Alaska Airlines.

He first joined the Alaska Air Group in 2001 as a first officer with Horizon. In 2012, Emerson left Horizon and joined Virgin America as a pilot.

After Alaska Airlines acquired Virgin America in 2016, Emerson became a first officer with Alaska and worked about three more years to become a pilot for the airline, according to the airline statement.

"Throughout his career, Emerson completed his mandated FAA medical certifications in accordance with regulatory requirements, and at no point were his certifications denied, suspended or revoked," Alaska Airlines said in a statement.

FAA records show Emerson held an Airline Transport Pilot certification with ratings to fly the Airbus A320, Boeing 737, Canadair Regional Jet, and De Havilland Dash 8. He did not hold a certification to fly the ERJ 175, those records indicate, the type of airplane in use during Sunday's incident.

CNN's Lauren Mascarenhas, Dakin Andone, Taylor Romine, Holmes Lybrand, Sarah Moon, Jeffrey Kopp and Veronica Miracle contributed to this report.