Investigators at Fort Hood, Texas, are looking into whether Maj. Nidal Malik Hasan acted alone in a shooting spree that killed 13 people, sources say.

Citing an unnamed law enforcement official in Washington, The New York Times reported Saturday that an early search of Hasan's computer didn't reveal any direct exchanges with known terrorists before he allegedly opened fire at the base, wounding at least 30 others in addition to the fatalities.

But the official also said investigators had yet to gain a complete record of Hasan's Internet use, noting he had multiple e-mail accounts and had used computers in several locations, the Times reported.

The newspaper said the FBI became aware of an Internet writer by the name of Nidal Hassan who had posted comments that seemed to view suicide bombings in a favorable light. But they are not sure if the postings were from the 39-year-old Army psychiatrist accused in the shooting spree.

Hassan -- shot four times -- remained on a ventilator Saturday.

Sen. Kay Bailey Hutchison, R-Texas, said Friday it was still unclear if Hasan had acted alone, telling the Times, "That is not a question that has been resolved."