WASHINGTON, March 22 (Reuters) - The U.S. Federal Bureau

of Investigation has told passengers who were on an Alaska

Airlines Boeing 737 MAX 9 that suffered a Jan. 5 mid-air

emergency that they may be victims of a crime, according to

letters seen by Reuters.

The letters, a procedural step in some criminal

investigations by the Justice Department, are a sign that its

probe into the MAX 9 emergency is moving forward.

The letters, dated Tuesday, say the FBI has identified the

passengers "as a possible victim of a crime. This case is

currently under investigation by the FBI. ...A criminal

investigation can be a lengthy undertaking, and, for several

reasons, we cannot tell you about its progress at this time."

The letters were earlier reported by the Seattle Times.

An FBI spokesperson in Seattle declined to comment, citing

Justice Department policy that it "does not confirm or deny the

existence of an investigation."

The Justice Department in 2022 updated its guidelines for

notifying victims of potential crimes after relatives of some of

the 346 people killed in two Boeing 737 MAX 8 crashes in 2018

and 2019 said their legal rights had been violated when the

department struck a January 2021 deferred prosecution deal with

Boeing ( BA ) without notifying them.

The department also apologized for not meeting with

relatives of the crash victims before the announcement of the

deal which capped a 21-month investigation into the design and

development of the 737 MAX 8.

Boeing ( BA ) declined to comment on Friday but said this month

said it would continue to cooperate fully and transparently with

all government investigations.

Alaska Airlines said it was fully cooperating with the

investigation and does not believe it is the target of the

probe.

In the midair emergency, a door plug panel tore off from the

side of the MAX 9 jet at 16,000 feet, leaving a

refrigerator-sized, rectangular hole in the aircraft. The plane

landed safely with all 171 passengers and six crew on board.

Seven passengers and one flight attendant had minor injuries.

The National Transportation Safety Board has said four key

bolts appeared to be missing from the plane that had been

delivered by Boeing ( BA ) months earlier. Boeing ( BA ) has said it believes

required documents detailing the removal of the bolts were never

created.

In the aftermath of the incident, the FAA grounded the MAX 9

for several weeks, barred Boeing ( BA ) from increasing the MAX

production rate and ordered it to develop a comprehensive plan

to address "systemic quality-control issues" within 90 days.