U.S. authorities believe suspected Fort Hood shooter Maj. Nidal Malik Hasan was most likely a self-radicalized extremist who acted alone, according to officials who were briefed on the case Tuesday.

The briefing for select members of Congress came as Republicans with oversight for national security issues called on Democratic House Speaker Nancy Pelosi to open a full congressional inquiry into alleged government miscues in the case of Maj. Hasan, who is charged with murdering 13 people Nov. 5 on the sprawling U.S. Army base where he served as a psychiatrist.

Military and FBI investigators cautioned lawmakers Tuesday that their probe is still in its early stages, according to people familiar with the briefings. But there did not appear to be any new information about alleged connections between Maj. Hasan and foreign or domestic extremists, cementing the early view that he acted alone, officials said.

House Intelligence committee chairman Silvestre Reyes (D., Texas) said that declaring Maj. Hasan a homegrown radical would be leaping to conclusions without sufficient facts. “It’s dangerous to speculate at this point when we know we don’t have all the facts,” he said in an interview.

Intelligence officials last year secretly intercepted communications between Maj. Hasan and a radical Yemeni cleric, but a subsequent probe by an FBI-led task force determined the psychiatrist, who treated emotionally wounded warriors, did not pose a terrorism threat.

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