EVERETT, WA (AP) – Boeing has refused to tell investigators who worked on the door plug that blew off a jetliner during flight in January.

The NTSB also claims that Boeing has not provided documentation about a repair job that included removing and reinstalling the panel on the Boeing 737 Max 9 or even whether Boeing kept records.

Boeing has been under increasing scrutiny since the Jan. 5 incident in which a panel that plugged a space left for an extra emergency door blew off an Alaska Airlines Max 9.

In a preliminary report last month, the NTSB said four bolts that help keep the door plug in place were missing after the panel was removed so workers could repair nearby damaged rivets last September.

The rivet repairs were done by contractors working for Boeing supplier Spirit AeroSystems, but the NTSB still does not know who removed and replaced the door panel.

Boeing has a 25-member team led by a manager, but they have declined repeated requests for their names so they can be interviewed by investigators.

The manager of the team is on medical leave and unavailable and security-camera footage that might have shown who removed the panel was erased and recorded over 30 days later.