Officers went to Cox-Brown's home and arrested him after finding a damaged vehicle missing pieces that matched those left behind at the crime scene.
In an interview with ABC affiliate KATU-TV, the owner of one of the damaged vehicles said what everyone watching the case was probably thinking: "Why would you post that? He basically just turned himself in."
Cox-Brown told KATU that his Facebook status update was "a big joke" and that he sideswiped the cars because of icy conditions. He is due in court April 22.
Shear, the social media law expert, said he would never allow a client to post anything like that online. But he argued that Cox-Brown's post alone would not be enough for a DUI conviction. Prosecutors would need additional evidence, such as a blood-alcohol-level report, he said.
"You want to focus on charging someone with something you can prove in the court of law," he said.
That may explain why police said Cox-Brown is charged not with driving under the influence but with two counts of "failing to perform the duties of a driver."
The Montreal Metro Drinking Marathon
A group of young partiers in Montreal gave authorities plenty of online evidence last month after a binge-drinking journey through the city's subways. The group participated in what they called the Montreal Metro Drinking Marathon, with plans to drink a beer at every station on the 30-stop Orange line.
They made it to 18 stations before losing focus, according to a post about it on Mook-life.com, a blog about youth culture in Montreal. "I guess alcohol got the best of us and we completely forgot what was going on at one point but in my opinion that makes us all winners!" said the March 25 post, which has since been taken down.
The group also posted photos, some with blurred faces, of members chugging beers on the trains and urinating at the subway stations -- both violations of city ordinances.
News sites republished some of the photos, and authorities took notice. Montreal police are now investigating the incidents and have asked for help in identifying the participants. A lawyer representing some of the partiers involved is negotiating with investigators, Montreal police said.
Canada and the United States have similar protections against suspects incriminating themselves while in custody, but voluntary gloating or confessions online are free game for law enforcement, legal experts said.
"What the Fifth Amendment protects against is compulsory confessions," Rozelle said. "No one compelled them to take photos of themselves drinking and peeing."
"The problem is that people don't realize that you can't take it back," added Shear. "It's almost impossible to unpost something."
When posting a photo is a crime
It's one thing to be arrested for posting a photo that shows you breaking the law. It's another to be arrested for posting a photo of someone else's handiwork.
In another case of social media consequences in Montreal, a woman was arrested earlier this month after she posted a photo on Instagram of graffiti she spotted on a city wall that depicted a high-ranking Montreal police officer with a bullet hole in his head. Jennifer Pawluck, 20, was accused of criminal harassment and intimidation, according to Montreal police.
"I think the person behind the artwork should be in my place ... all I did was take a photo," she told the Canadian Broadcasting Corporation.
Pawluck has not been formally charged but is scheduled to appear in court on May 24. A Montreal police spokesperson said there's more behind her arrest than just the posting of the photo, but declined to offer further details.
Legal experts say photos and videos, whether posted publicly online or obtained in a more discreet manner by the police, have to meet the same criteria: They must be authenticated, meaning the prosecutors must prove the images are what they seem and have not been altered or staged. And they can't be shown out of context.