EAST JERUSALEM – “I think it goes to flames.” Nuha Musleh, a Palestinian who earns her living as a “fixer” – a guide/translator/arranger for foreign reporters – stage-whispered that in my ear. We were standing on a sidewalk in Shuafat, a Palestinian neighborhood of East Jerusalem, watching a loud and angry demonstration in support of Muhammad Abu Khdeir, the 16-year-old boy abducted and murdered earlier two days earlier. The demonstrators blamed Israelis: an act of revenge, they presumed, for the kidnapping and killing of three Israeli teenagers last month, crimes Israeli officials have linked to Hamas.

Ms. Musleh was working for an Italian television crew whose camera was focused on young men with kefiyehs covering their faces. Some had knives tucked into their belts. Many carried flags: Palestinian nationalist flags; flags of the Popular Front for the Liberation of Palestine, a Marxist-Leninist terrorist organization; flags of Hizb ut-Tahrir, an international Islamist group intent on establishing a new caliphate; black flags similar to those al Qaeda displays. A few wore Guy Fawkes masks -- the kind favored by members of the nihilist/activist/ hactivist movement that calls itself Anonymous.

Shuafat does not appear to be a hopeless place. The home of the Abu Khdeir family -- a prominent family -- is large and stately, constructed of stone. Nearby are shops and a mosque. A sign advertises an orthodontist’s office.

But now the neighborhood is in shambles: strewn with rocks, teargas canisters, broken glass and garbage. The blisteringly hot air is redolent with smoldering tires.

A light rail line runs down the main street. It took years to build and cost millions of dollars. It was intended to serve as a bridge between Palestinian East Jerusalem and other sections of the city where some residents of Shuafat work, shop or visit friends. That bridge has now been burned -- literally. Equipment has been torn out and the shelters smashed as well.

How long before the line is repaired? Possibly never. Radical Palestinian groups say they won’t allow it. Expect other Palestinian groups to charge that, without the rail line, they are being cut off, that the Israelis are separating them, imposing “apartheid.”

The reason Ms. Musleh was predicting a further escalation of violence and destruction: Muhammad’s body was just then being carried to the mosque where the funeral would be held. After that, she told me, the shabaab, the young people, would be even angrier. It didn’t help that this was the first Friday of Ramadan, a period when, from sunup to sundown, observant Muslims may neither eat nor drink.

As the body arrived, in an open casket and wrapped in a Palestinian flag, there were sudden explosions. These turned out to be firecrackers, loud and smoky but not dangerous. Demonstrators chanted -- praising those who sacrifice for Palestine, and vowing to “Explode the skull of the Zionist.”

After the funeral, some demonstrators sought out Israeli soldiers and police – who had prudently stayed blocks away -- and threw Molotov cocktails, pipe bombs and rocks at them. Teargas, stun grenades and rubber bullets were fired in return. People on both sides were hurt but, according to press reports, no one lethally.

It may have helped that Palestinian leaders, including Mahmoud Abbas, had called for restraint, and that Israeli leaders, not least Benjamin Netanyahu, had unequivocally condemned the murder of the Palestinian teenager, promising to bring to justice “the criminals responsible for this despicable crime, whoever they may be. Murder, riots, incitement, vigilantism — they have no place in our democracy."

On Sunday, Israeli authorities arrested six suspects. An Israeli official described them to a French news agency reporter as members of an “extremist Jewish group.” According to other reports several were “soccer hooligans” with criminal records. It was not clear whether they belonged to a loose network of vigilantes known as “Price Tag” – the name signifying that its members intend to make Palestinians pay for acts of terrorism. In the past, however, Price Taggers have generally gone no further than spray-painting mosques with hostile slogans, uprooting trees or puncturing the tires of Palestinian cars. Kidnapping a teenage boy, burning him alive and leaving his body in a forest would represent an astonishing escalation.

A friend, an Israeli college professor, called this latest development – let’s not mince words: this brutal terrorist act committed by an Israeli -- “devastating,” causing “paroxysms of self-examination” within Israel. A prominent writer called it “the lowest moment in the history of Israel.”

It’s also true, however, that Israeli authorities investigated the crime aggressively and made arrests quickly. The prosecution that follows is expected to be unsparing. The vast majority of Israelis will not regard anyone found guilty as a hero or martyr. Salaries will not be paid to them when they are incarcerated (as is the case with Palestinian terrorists in Israeli prisons).

By contrast, the murders of the three Israeli teenagers have been widely celebrated in the West Bank and Gaza – places where streets are named for suicide bombers. Palestinian media have compared the Jewish boys to vermin – therefore deserving of extermination. Mr. Netanyahu has suggested that the Palestinian Authority is doing little to help Israeli law enforcement locate and apprehend the killers.

Many pertinent facts have yet to emerge about both cases. When they do, it may not make much difference. Many people believe what they choose to believe, regardless of the facts. In Jerusalem, an ancient city built on beliefs and believers, that may be especially true.

Clifford D. May is president of the Foundation for Defense of Democracies (FDD), a policy institute focusing on national security.