The second black box from China Eastern Airlines Flight 5735 was found Sunday as investigators try to piece together what caused the passenger plane to plunge straight into the ground, killing all 132 on board.

The second black box, the flight data recorder, was discovered at the crash site about 1.5 meters under the soil at about 9 a.m. local time, according to state-owned media outlets CCTV and Xinhua.

The first black box was recovered on March 23. The first black box contained the voice data recorder, according to an official from the Civil Aviation Administration of China.

The flight data recorder was found on the eastern side of the impact crater, according to state-run media, which is 100-feet wide and 66-feet deep.

The crash as been a mystery to investigators, including officials from the U.S. National Transportation Safety Board and Federal Aviation Administration, who are joining Chinese agencies looking into the crash.

Early data shows the airliner plunged from 29,000 feet to 8,000 feet, leveled off and then went into a freefall, exploding into a fireball. One video showed the plane nose-diving into the ground.

U.S. intelligence doesn’t have a clear theory on what led to the plane crashing. A source told ABC News they aren’t ruling anything out, including a possible intentional downing.

The plane crashed after taking off from Kunming, the capital of China’s Yunnan province. The flight was headed to Guangzhou, a city northwest of Hong Kong, Chinese officials said.

While all 123 passengers and nine crew members were presumed dead soon after the crash, Chinese officials confirmed Saturday there were no survivors. State media said 120 of the victims had been identified through DNA testing.

“We extend our deepest condolences for the loss of those on board China Eastern Airlines Flight MU 5735,” Boeing said in a statement. “Our thoughts and prayers are with the passengers and crew, their families and all those affected by this accident. Boeing will continue to support our airline customer during this difficult time. In addition, a Boeing technical team is supporting the NTSB and the Civil Aviation Administration of China who will lead the investigation.”

Boeing deferred questions on the investigation to the CAAC.

ABC News’ Karson Yiu, Bill Hutchinson, Amanda Maile and Josh Margolin contributed to this report.