SAN FRANCISCO — A routine Delta flight turned anything but ordinary after landing at San Francisco International Airport Saturday night.

Delta Flight 2809 had just arrived from Minneapolis when, according to passengers, a group of federal agents suddenly boarded the plane and stormed the cockpit.

“We were all shocked and stunned. What was happening?” passenger Sarah, who didn’t want her last name to be identified, told ABC San Francisco affiliate KGO.

Sarah, who frequently travels this route, said passengers had just started to gather their belongings from the overhead bins when the agents rushed in.

“They barged through and stormed the cockpit,” she said. “They removed the co-pilot, cuffed him, presumably arrested him, and brought him back down the aisle to deplane.”

She counted at least 10 agents on board, some wearing badges she recognized from the Department of Homeland Security.

KGO reached out to the Department of Homeland Security. A spokesperson referred our inquiry to the U.S. Attorney’s Office. As of Sunday night, we are still awaiting a response. Delta Airlines also referred our inquiry to law enforcement.

“I don’t know if this person was disappearing before our eyes, if there had been a crime committed, or what exactly was happening,” Sarah said. She added that fellow passengers, flight attendants and even the remaining pilot appeared just as confused by the situation. Despite arriving safely, the incident stayed with her long after she left the airport.

“It was scary. It was traumatic to watch,” she said. “As soon as my husband picked me up from baggage claim, I jumped in the car and cried. Because who knows what’s happening to that poor person? Why that happened? What did we just see?”

This dramatic incident comes amid a string of recent airline-related scares:

A grandmother on another Delta flight says she stopped a fellow passenger from trying to enter the cockpit.

A Southwest flight descended rapidly to avoid a Hawker Hunter aircraft, leaving passengers frightened.

And on Sunday, passengers aboard an American Airlines flight out of Denver were forced to evacuate shortly after takeoff.

As for what exactly happened aboard Delta Flight 2809, passengers, and the public, are still waiting for answers.

“It’s just a huge question mark,” Sarah said. “And we need to know what happened.”