[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/04/15/art.collins.jkusa.jpg caption ="Sen. Susan Collins is leading an investigation into last November's mass shooting at Fort Hood."]Washington (CNN) - A top GOP Senator promised Thursday to subpoena the Obama administration if they fail to provide information sought in a Congressional investigation into last November's mass shooting at Fort Hood.
Sen. Susan Collins of Maine, the ranking Republican on the Senate Homeland Security Committee, said the Obama administration is "stonewalling" their investigation.
Both Collins and Sen. Joe Lieberman, the chairman of the committee, have been trying since November to obtain information from the Justice and Defense Departments about the shooting rampage, in which Army Major Nidal Malik Hasan killed 13 people.
"It makes you wonder if the White House doesn't want to hear what we're going to find about inadequate information sharing between the FBI and DoD, information that had it been shared might have prevented this tragedy," Collins said on CNN's "John King USA."
Though the administration has provided some details about the shooting, officials have said that turning over more information could compromise their case against Hasan.
But Collins said she is "puzzled" as to why the administration is not cooperating. She said subpoenas will be issued to the Justice and Defense Departments on Monday if information about the shooting is not turned over.
"Issuing a subpoena is a last resort," she said. "We don't want to do that. We want to have a cooperative arrangement with the administration, but after five months, we have reached the conclusion that we have no other choice if we are to carry out our obligation to exercise oversight."
Collins said the goal of the investigation is to improve information-sharing procedures in order to prevent future acts.
"Until we find out why essential information was not shared between the FBI and the Army, we can't be sure it won't happen again," Collins said.