Boeing overwrote surveillance footage from the repair facility where a door plug was reinstalled ahead of the blowout on an Alaska Airlines flight earlier this year, according to a letter Wednesday from National Transportation Safety Board Chairman Jennifer Homendy to the Senate Commerce Committee.

The NTSB had been requesting the footage in order to investigate what happened during the midflight scare.

The NTSB still does not know which Boeing employees worked on the failed door plug of Alaska Airlines 1282, which had its door plug blow out during a flight in January, Homendy also said in the letter.

“To date, we still do not know who performed the work to open, reinstall, and close the door plug on the accident aircraft,” Homendy wrote to Sens. Maria Cantwell and Ted Cruz. “Boeing has informed us that they are unable to find the records documenting this work.”

Boeing said in a statement Wednesday that it will continue to support the NTSB’s investigation “in the transparent and proactive fashion we have supported all regulatory inquiries into this accident.”

“We have worked hard to honor the rules about the release of investigative information in an environment of intense interest from our employees, customers, and other stakeholders, and we will continue our efforts to do so,” the statement continued.

During her hearing in front of the committee earlier this month, Homendy informed lawmakers that Boeing had not yet handed over documents needed in their investigation, including the names of 25 people who worked on the door plug.

After NTSB investigators initially requested the documents on Jan. 9, they learned the door crew manager was out on medical leave, according to Homendy. They requested updates on Feb. 15 and Feb. 22, though were informed by the manager’s attorney that “he would not be able to provide a statement or interview to NTSB due to medical issues,” Homendy wrote in her letter.

Following the March 6 hearing, Boeing provided a list of names to the NTSB of personnel who reported to the door crew manager, but that list did not identify who performed the door plug work, according to Homendy.

Homendy stated in her letter that she then contacted Boeing CEO Dave Calhoun after receiving the list and asked for the names of those who performed the work. Calhoun “stated he was unable to provide that information and maintained that Boeing has no records of the work being performed,” according to Homendy’s letter.

“The absence of those records will complicate the NTSB’s investigation moving forward,” Homendy wrote in the letter, which was requested in response to questions during her testimony in front of the committee.

Homendy insisted in the letter that her agency is “not in any way seeking the names of employees who performed the work on the door plug for punitive purposes” — saying she instructed the NTSB to protect the identities of the door crew and other front-line employees who come forward.

Following the hearing, Boeing said in a statement to ABC News that the company has responded “comprehensively” to all NTSB requests with relevant information.

“Early in the investigation, we provided the NTSB with names of Boeing employees, including door specialists, who we believed would have relevant information. We have now provided the full list of individuals on the 737 door team, in response to a recent request,” the statement said. “With respect to documentation, if the door plug removal was undocumented there would be no documentation to share.”

“We will continue to cooperate fully and transparently with the NTSB’s investigation,” the company said.

The door plug of Alaska Airlines flight 1282 fell off a few minutes after take off from Portland International Airport on Jan. 5. Passengers captured footage showing a hole where the door plug came loose on the Boeing 737 Max 9 plane. The plane safely made an emergency landing and no one was seriously injured.

An NTSB preliminary report released last month found that four bolts designed to prevent the door plug from falling off the Boeing 737 Max 9 plane were missing before the plug blew off the flight.

The NTSB will hold a two-day investigative hearing on the door plug incident in August, the agency announced on Tuesday.

The investigating hearing will “assist in obtaining information necessary to determine the facts, circumstances, and probable cause of the transportation accident or incident under investigation and to make recommendations to improve transportation safety,” the NTSB said in a statement.

The agency held similar hearings last year on the toxic train derailment in East Palestine, Ohio.