Los Angeles, California - The FBI has written to passengers who were aboard a Boeing aircraft that suffered a midair accident to tell them they may be victims of a crime, US media reported Friday.

The move comes after the Department of Justice earlier this month announced it was opening a criminal investigation into the near-catastrophic incident on January 5, when a panel blew off the fuselage of an Alaska Airlines-operated plane mid-flight.

No one was seriously hurt, but the 737 MAX 9 had to make an emergency landing, with footage showing the terrifying scene as passengers sat next to the gaping hole.

The so-called door plug landed in a suburban backyard.

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The incident resulted in planes with similar configurations being temporarily grounded, forcing thousands of flights to be canceled.

"As a Victim Specialist with the Seattle Division, I'm contacting you because we have identified you as a possible victim of a crime," the FBI letter sent to passengers said, according to the Seattle Times, which said it had seen the document.

"This case is currently under investigation by the FBI," the letter said. "A criminal investigation can be a lengthy undertaking, and for several reasons, we cannot tell you about its progress at this time."

Federal investigators say bolts that should have secured the panel – a covering for an optional exit – were not installed.

Aviation giant Boeing has been criticized for dragging its heels in the probe, with the National Transportation Safety Board (NTSB) saying at the start of March it had not received key documents or the names of Boeing employees who worked on the part in question.

"We don't have the records. We don't have the names of the 25 people in charge of doing that work in that facility," NTSB Chair Jennifer Homendy told US lawmakers.

"It's absurd that two months later we don't have that."