SYRIAN DICTATOR Bashar al-Assad has benefited substantially from the difficulty the world’s media have had in reporting on the protest movement in Syria and the regime’s brutal suppression of it. Foreign journalists are banned from Syria and anyone attempting to film or otherwise report on events since mid-March has been subject to arrest and torture by security forces.

But Mr. Assad does not live in the world of his father, whose massacre of tens of thousands of people in the city of Hama in 1982 was not fully reported to the outside world for months. Today brave Syrians have managed to post hundreds of cellphone videos to the Internet, documenting the regime’s practice of assaulting unarmed civilians with tanks, artillery and automatic weapons. One showing the mutilated body of 13-year-old Hamza Ali al-Khatib, who was arrested and murdered by security forces, has horrified the world and inspired more protests across Syria.

On Wednesday, Human Rights Watch made an important contribution to knowledge about the events in Daraa, a town and its surrounding province in southwestern Syria where mass protests first erupted on March 18. Based on interviews with more than 50 residents and a review of dozens of videos, the group concluded that at least 418 people have been killed there over the course of 10 weeks and that the regime’s “abuses qualify as crimes against humanity.”

The report is stomach-turning in its account of what was inflicted on the community of 80,000 and its suburbs. The trouble began, it says, when 15 young boys, aged 10 to 15, were arrested for anti-regime graffiti; when they were finally released, they were “bruised and bloodied after what they described as severe torture in detention.” As mass protests swelled, “security forces deliberately targeted protesters,” who bared their chests and carried olive branches to show their peaceful intentions. A mosque where many took refuge was assaulted on March 23, leading to the deaths of 30.

On April 25, an 11-day siege of the city began, during which anyone taking to the streets — including children seeking food or medicine — was fired on by troops or rooftop snipers. When thousands of people marched on the town April 29 in an effort to break the siege, troops again opened fire, killing at least 62, according to the report.

Two of the witnesses interviewed by Human Rights Watch were among thousands detained in Daraa’s soccer stadium on May 1 when, they said, security forces arbitrarily selected a group of more than 20 young men, lined them up and gunned them down. Other witnesses described an incident in which several soldiers who refused to shoot at protesters were themselves shot and killed.

Partly due to the limited information, the world is reacting slowly to these atrocities. The State Department called the case of Hamza Ali al-Khatib “horrifying” and “appalling,” but U.S. policy, restated by Secretary of State Hillary Rodham Clinton on Tuesday, remains a “hope” that “the Syrian government will end the brutality and begin a transition to real democracy.” Ms. Clinton ought to read the Human Rights Watch report. No one who does so could propose such an outcome with a straight face. Perhaps the United States cannot intervene to save Daraa, as it did the Libyan city of Benghazi. But the focus of its policy should be holding Mr. Assad accountable for these crimes — and not pretending that he can become a legitimate ruler.