Just two weeks after a day-long party celebrating its selection as host city for the 2016 Summer Olympics, it’s back to business as usual for Rio de Janeiro: Rampant gang violence resulting in multiple deaths. The photo below shows a police helicopter that was shot down by one of the drug gangs, crash-landing on a soccer field and killing three policemen who were on board.

You know your town has a gang problem when they’re shooting down helicopters. Savvy choice, IOC. I can see the postcards now: “Having a great time at the Olympics. Except for that part when a plane was shot down over Landon Donovan.”

Violence between two of Rio’s biggest drug gangs this weekend left 21 dead in the Morros de Macacos slum, including the three policemen who died in the crash. Brazilian President Luiz Inácio Lula da Silva promised to deploy federal police and allocate $60 million in aid to “clean up the mess left by the gangs,” which would be nice. Because they have to start, like, building a place to hold rhythmic gymnastics.

Police officials said they recovered at least one high-caliber machine gun capable of shooting down a helicopter. Violence isn’t unusual in Rio, where the murder rate places it among the world’s most dangerous cities.

But Rio’s successful campaign to host the 2016 Olympics has brought new urgency to the issue. Proponents of the city’s bid convinced Olympic officials that the city would keep spectators and athletes safe with an increased police presence and other measures.

The city will also host key matches when Brazil hosts soccer’s World Cup in 2014.

Just a few weeks ago, while marshaling support for Rio’s Olympic case during a news conference in New York, Mr. da Silva played down concerns about crime. Brazilians will be in such a “state of grace” during the Olympics that crime won’t be an issue, he told reporters.

(Two buses in “state of grace” after being torched by gangs on Sunday)

Whether you’re a fan of the Rio pick or not, it’s clear that it’s probably the biggest gamble the IOC has ever made. This can be a huge success story — and a great example of what the Olympics is about — if Rio can rise from the rubble of crime and pollution and rebuild itself around the Olympic construction effort. But it will be a monumental task, and as recent events have proven, things can go horribly wrong.

Was the IOC sold a bill of goods on Oct. 2?

In an evaluation report issued a month before Rio’s victory in Copenhagen, the IOC said Rio faced “safety challenges” but that community police programs had produced “positive results” in reducing crime.

“IOC members voted on the basis of an evaluation commission report that invited them to disregard (crime) as a serious factor,” said Canadian IOC official Dick Pound. “It was basically telling the membership not to worry about that.”

And, they’re not. At least for now.