An investigation into the recent crashes of two Boeing 737 MAX jets includes the unusual aspect of criminal subpoenas. The Associated Press and NBC News reports that criminal grand jury subpoenas were issued to the Federal Aviation Administration to preserve documents and emails about the plane’s certification.

“It’s not without precedent, but it’s highly unusual,” said James Anderson of the Aviation Law Group in Seattle. He is not connected with any of these cases but echoes what other aviation experts have been saying, that criminal charges are usually not brought in connection with accidents happening in the U.S. or within the U.S. involving overseas accidents.

"One of the biggest concerns, is whether witnesses are going to be interested in helping out. If they’re going to be under criminal investigation, and whether they would, for example, be willing to invoke the fifth amendment and refuse to answer questions. Because perhaps they are a criminal suspect,” said Anderson.

The U.S. and Canada have a different approach than many other countries that start all accident investigations with a criminal probe. Anderson and other U.S. aviation experts say by not criminalizing the process, by allowing the National Transportation Safety board to take the lead in U.S. investigations, accidents and their root causes can be determined sooner, recommendations can be made quicker and similar accidents can be prevented.

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Anderson added, “If you have an NTSB investigation and a criminal investigation going on at the same time, you may have investigators competing for evidence.” 

He believes the 1996 Value Jet accident where a DC-9 went down in the Florida Everglades was hampered because the question of an unlabeled load of flammable oxygen generators shipped as cargo was pursued on a criminal basis.