Speaking on an internet video released by the White House on Saturday, Barack Obama said the deaths of 13 people should not be used to create "political theatre" as "the stakes are far too high".
The man charged with the murders, Major Nidal Malik Hasan, an army psychiatrist, had previously been investigated by authorities and was suspected of links to a Muslim religious leader in Yemen.
Some members of congress have called for their own investigation into what intelligence agencies knew of Hasan's contacts and suggest the administration is being guarded with the facts.
Obama has already ordered a review of what was known and whether information was correctly shared and acted upon.
Peter Hoekstra, the most senior Republican party official on the House intelligence committee, said last week that Hasan and the religious leader had exchanged at least 10 emails from December 2008.
A Federal Bureau of Investigation terrorism task force knew last year of the pair's communication but decided that it was not linked to terrorism.
Al Jazeera (English)