Searchers combing a shallow Texas bay have recovered the second of two flight recorders from a cargo plane hauling Amazon packages that crashed last week, the National Transportation Safety Board said on Sunday, two days after finding the first.

The NTSB said in a tweet it had recovered the second crash-proof cockpit voice recorder. The Boeing Co. 767-300 dove abruptly and went down on Feb. 23, killing two Atlas Air pilots and a third pilot who was riding in the jump seat. The recording of cockpit sounds could help investigators determine why the plane went down as it was approaching Houston.

Both flight data recorders are being transported back to the NTSB’s labs in Washington for evaluation.

The Atlas plane was one of 50 aircraft under contract to Amazon.com Inc. to haul packages for the online retailer. Atlas is a subsidiary of Atlas Air Worldwide Holdings Inc.

After what had been a routine descent while preparing to land at Houston’s George Bush Intercontinental Airport, Atlas Flight 3591 abruptly dove thousands of feet into Trinity Bay. There was no emergency radio call by pilots and nothing has emerged to explain whether it was a mechanical failure, actions by pilots or some other problem that led to the plunge.

The cockpit recorder would have captured pilot conversations as well as ambient noise from the flight deck.

Search teams are continuing to try to find a second device, known as a flight data recorder, that stores data on a plane’s systems, actions by the pilots and a detailed flight path.