The terrorist who opened fire on a bus in Shfaram was an Israel Defense Forces deserter and a radical right-wing West Bank settler.

The gunman, Eden Natan-Zada, 19, reportedly moved recently from Rishon Letzion to the Tapuach settlement, where he was in contact with members of the outlawed extreme-right Kach movement. The Shin Bet's Jewish Division has maintained a file on Natan-Zada.

Having changed his name to Tzubeiri, Natan-Zada enlisted in the IDF in January and underwent basic training at the Nitzanim base.

IDF sources said yesterday that Natan-Zada was a problematic soldier from the outset, and had been arrested twice for going AWOL. In mid-June, when he was ordered to take part in building the "tent town" in Re'im for soldiers participating in the Gaza Strip evacuation, he refused to carry it out.

Shortly afterward, he defected from the army in what was described as an "ideologically based" desertion to protest of the disengagement. Natan-Zada, who was AWOL for more than a month and a half, kept his IDF-issued rifle.

He settled in Tapuach, a hub for Kach activists, including many who immigrated from the United States. According to unconfirmed reports, Natan-Zada is newly religious.

The Shin Bet yesterday launched a probe into what the security service knew about Natan-Zada, who was under the Jewish Division's surveillance. The Shin Bet will investigate whether Natan-Zada's desertion, his relationship with Kach, and his place of residence did not warrant a closer watch.

Chief of Staff Brigadier General Dan Halutz yesterday ordered an inquiry into how Natan-Zada's rifle remained in his possession given his problematic background.

At the same time, the Military Police will help the Shin Bet and police in investigating the affair.

Halutz denounced the terrorist attack, which he called "a heinous murder."

IDF sources said Natan-Zada's commanders tried to locate him after he went AWOL, and contacted his family in an attempt to reach him.

The sources expressed fear that the murder would inflame spirits in the West Bank as well. The Central Command raised the alert level before today's prayers in the mosques, fearing mass demonstrations and revenge attacks by Palestinians. The army also is expected to beef up its forces, especially in the Machpela Cave in Hebron, which is considered a trouble spot.

The Southern Command has been asked to return some of the forces, including Border Police units, that were moved to the south for this week's right-wing demonstration in Ofakim.

Only a few of Tapuah's residents knew Natan-Zada. Settlers there said he did not live there, but only visited friends.

One of his friends, who wished to remain anonymous, said that Natan-Zada, who came from a traditional Persian family, found friends in Tapuah with whom he studied the Torah.

"Eden was a serious guy, not reckless, and if he decided to do such a thing, then it was after consideration - not on a whim or due to depression, but for ideological reasons."

The Tapuah secretariat yesterday issued a strong denunciation of the murder. Secretariat member Levy Ben Zion said Natan-Zada did not live at the settlement, although he may have visited occasionally. "Someone like that would not have been accepted here," he said.

"We have an absorption and selection committee, and we don't accept radical people. We've had enough of them. We strongly denounce the murder of innocent people."