The Department of Justice has opened a criminal investigation into the door plug blowout on an Alaska Airlines-operated Boeing 737 Max 9 flight in January, The Wall Street Journal reported Saturday.

The Wall Street Journal, citing “documents and people familiar with the matter,” reported that the DOJ has contacted some passengers who were on the flight to notify them that they are potential victims in the criminal investigation, and that the agency has interviewed pilots and flight attendants who were on the flight.

Both the Justice Department and Boeing said they had no comment on the investigation.

“In an event like this, it’s normal for the DOJ to be conducting an investigation,” Alaska Airlines said in a statement, adding that it is “fully cooperating and [we] do not believe we are a target of the investigation.”

On Jan. 5, Flight 1282 departed Portland International Airport for Ontario International Airport in San Bernardino County, California, but turned back after a portion of the plane’s fuselage, known as a “door plug,” detached shortly after takeoff. No one on board was seriously injured and the plane landed safely, but officials cautioned that the situation could have been “much more tragic.”

The incident prompted the temporary grounding of some Boeing 737 Max 9 airplanes. Planes have since returned to service.

An investigation led by the National Transportation Safety Board preliminarily found there were no bolts installed on the door plug.

According to The Wall Street Journal, investigators are looking into whether Boeing complied with a settlement following the 2018 and 2019 737 Max 8 crashes that claimed the lives of 346 people.

The DOJ ultimately placed blame on Boeing in those cases, which in turn blamed two former pilots who determined the amount of training needed to fly the Max planes.

Boeing was ordered to pay $2.5 billion to settle the investigation in 2021, and the government said it would drop a charge of conspiracy to defraud the U.S. after three years if Boeing followed the terms of the settlement.

According to The Wall Street Journal, Boeing could face prosecution on the original count of defrauding the U.S. if, in this new case, the DOJ finds Boeing is at fault of violating the terms of the 2021 settlement. The government could also extend a three-year probationary agreement requiring Boeing to keep the DOJ updated on compliance improvements, the Journal reported.

Following the January Alaska Airlines incident, a number of passengers filed suit against the airline and Boeing.

In the days following the blowout, seven passengers filed a class-action lawsuit against Boeing, alleging the company “delivered the subject 737 MAX-9 to Alaska Airlines, Inc. without properly securing the [door] plug to the airframe,” or because the bolts and seals used to install the panel were defective.

In February, three passengers filed a $1 billion lawsuit against Alaska Airlines and Boeing, accusing the companies of negligence and alleging they ignored warning signs that could have prevented the door plug fiasco.

Jonathan Johnson, a lawyer representing those passengers, said in a Saturday statement, “We are pleased that DOJ has opened this investigation to help determine why this plane was not properly manufactured.”

He added that he hopes “those responsible will be held accountable.”

This week, the Federal Aviation Administration said an audit of Boeing and Spirit AeroSystems — which made the plane at the center of January’s incident — “found multiple instances where the companies allegedly failed to comply with manufacturing quality control requirements.”