Federal prosecutors investigating the Jan. 5 midair blowout of a Boeing Co. door plug on an Alaska Airlines flight are casting a wide net to gather information and documents, sending subpoenas and using a grand jury based in Seattle.

The US Attorney for the Western District of Washington has convened a “grand jury investigation of suspected violations of federal criminal laws,” according to a copy of a subpoena reviewed by Bloomberg News.

The subpoena seeks documents and communications related to Boeing and Spirit AeroSystems Holdings, as well as references to the “door plug” used in the Boeing 737 Max 9 aircraft. 

In addition, prosecutors appear to be interested in any correspondence and records between Boeing and a number of Max 9 operators aside from Alaska Airlines, said a person familiar with the matter. A Boeing plane operated by the Seattle-based carrier suffered a perilously close call in January after a fuselage panel blew out minutes after take-off.

The Justice Department is taking an aggressive approach with its criminal investigation into the midair blowout. Along with the US attorney’s office in Seattle, the department’s fraud section in Washington is probing the incident.

A Boeing spokeswoman and the Justice Department declined to comment.

The department appears to be operating on two tracks. It’s looking into whether the door plug blowout falls under and violates the government’s 2021 deferred-prosecution agreement with the company over two previous fatal crashes of its 737 Max jetliner. The department also could determine there’s enough evidence to consider the Jan. 5 incident as a standalone criminal investigation.