JERUSALEM -- The young man making his way along the Street of the Prophets was dressed in a skullcap, white shirt and dark trousers -- the sober garb of an Orthodox Jew, apparel that would scarcely draw a glance in the center of Jerusalem.

But to sharp-eyed passers-by, the man's demeanor was all wrong. His movements were jerky, nervous; he was almost running. As two Israeli paramilitary policemen confronted him, he smiled, turned away -- and detonated explosives in a sack strapped to his back.

Even in bomb-hardened Jerusalem -- where the previous 36 hours had produced no fewer than four blasts, none causing serious injury -- the gruesome aftermath of this attack had the power to shock.

The force of the explosion catapulted the bomber's severed head over a high wall and into the schoolyard of a French school as children were arriving for class. Scraps of flesh were embedded in the cracks of the former convent's high stone wall.

Bystanders, including at least one arriving schoolgirl, were pelted with bloody bits of the bomber's body. Others suffered shrapnel wounds from nails and screws packed into the bomb.

Twenty injured

Twenty people were injured, including the two paramilitary border policemen. One was in critical condition following surgery for internal injuries and severe burns, and his young partner was inconsolable.

"He was just ahead of me -- he took the force of it," said 24-year-old Guy Mughrabi, red-eyed and dressed in a wrinkled hospital smock, speaking to reporters from his bed in a hospital just up the street from the blast site.

With an iodine-soaked bandage showing under the open neck of his hospital gown where he was hit by shrapnel, Mughrabi recounted how the pair spotted the man moments after being alerted that someone suspicious was in the area.

"We yelled 'Stop!'" Mughrabi said. "He had this smile on his face that I will never forget. We raised our rifles. We knew this was a point of no return, that we had a suicide bomber in front of us."

The explosion scorched the high outer walls of the Lycee Francais, a French-language international school. Pierre Weill, a Radio France correspondent, had just pulled up outside the school to drop off his 12-year-old daughter Ines when the thunderous blast shook the street.

"My car was splattered with pieces of flesh and blood. My daughter was also covered with bits of flesh and blood," he said. "We saw the head of the suicide bomber rolling into the courtyard."

Police quickly covered the head with an upended trash can, but not before some of the children saw it. Classes went ahead despite the bombing.