OCEAN CITY, Md. (WJZ) — The investigation into a tragic Ocean City plane crash that killed two off-duty police officers continues.

Gigi Barnett explains–the next step in the probe is determining what happened.

Transportation investigators have eyewitness accounts from the beach in Ocean City, where a recreational plane did a nosedive into the water, killing two off-duty officers inside.

Now, they’re piecing together the wreckage pulled from the shore and trying to answer tough questions.

“The investigation has moved into the federal phase, as federal investigators examine the aircraft and try to determine what happened and why it happened,” said Greg Shipley, Maryland State Police.

On board were Ocean City officers Tom Gaygan and Joshua Adicks–off for a day of fun in the skies on Sunday.

Rescue workers found their bodies about a quarter mile from the shore, and the plane 30 feet deep.

Folks on the beach saw everything.

“I was shocked. From here, I looked up at the lifeguard and I was like, ‘Please tell me that was a toy remote control airplane.’ And he was like, ‘No, it was a real plane,'” said Melissa Mitchell, witness.

Maryland State Police Spokesman Greg Shipley says emotions among members of the Ocean City Police Department are high.

“It has certainly hit the Ocean City Police Department hard. The loss of not one, but two lives in this way. Both very well liked officers who were dedicated to their jobs there. It’s a difficult time for them,” said Shipley.

NTSB investigators say it could take months before they determine the exact cause of the crash.

The Federal Aviation Administration is also looking into the cause of the crash.