Senators looking into the November shooting rampage at Fort Hood served the Pentagon and U.S. Justice Department with subpoenas Monday demanding key documents and access to witnesses.
Senate Homeland Security and Governmental Affairs Committee Chairman Joe Lieberman, an independent, and the panel's top Republican, Sen. Susan Collins, had warned last week they would take such a step.
Lieberman and Collins have sought documents including the personnel file of the accused shooter, Major Nidal Hasan, and any documents showing he communicated with a radical Islamic cleric in Yemen, Anwar al-Awlaqi.
In a letter to Defense Secretary Robert Gates and Attorney General Eric Holder, the senators said they were "frustrated" with both departments' "failure" to provide the information voluntarily.
"Unfortunately, it is impossible for us to avoid reaching the conclusion that the departments simply do not want to cooperate with our investigation," they wrote.
"Given the warning signs of Major Nidal Malik Hasan's extremist radicalization and growing hostility toward the U.S. military and the United States generally, why was he not stopped before he took 13 American lives," they wrote.
"How can we prevent such a tragedy from happening again?" wrote the senators, whose subpoenas demand the information by 10 a.m. on April 26.
At the Pentagon, spokesman Bryan Whitman said officials "will obviously be reviewing it (the letter) and determine the department's next steps."
But Pentagon legal experts made clear in a background briefing for reporters that the U.S. military would not necessarily cooperate with the subpoena if it believed that doing so might harm the prosecution of Hasan.
"If we reach conclusion that the request for information would jeopardize the military justice process, one option is say no," said one expert. "Another option is re-engage with the committee and see if you can work out some alternatives."
Hasan's military trial "could last much of 2010," said the expert, who spoke on condition of anonymity.
© AFP 2013