CAIRO — Hamza Ali al-Khateeb, a round-faced 13-year-old boy, was arrested at a protest in Jiza, a southern Syrian village near Dara’a, on April 29. Nothing was known of him for a month before his mutilated corpse was returned to his family on the condition, according to activists, that they never speak of his brutal end.

But the remains themselves testify all too clearly to ghastly torture. Video posted online shows his battered, purple face. His skin is scrawled with cuts, gashes, deep burns and bullet wounds that would probably have injured but not killed. His jaw and kneecaps are shattered, according to an unidentified narrator, and his penis chopped off.

“These are the reforms of the treacherous Bashar,” the narrator says. “Where are human rights? Where are the international criminal tribunals?”

In Syria and beyond, the youth’s battered body has cast into shocking relief the terrors wielded by the Syrian state against its people.