When the unrest broke out last April, police pushed back against protestors with more than just riot gear, officers were tracking posts on social media in certain areas of the city. Law enforcement may have also put pictures through facial recognition software to arrest people in the crowd with outstanding warrants.
"This was a betrayal of the trust that I think most users thought they had with these social media platforms," said David Rocah, senior staff attorney for the ALCU of Maryland.
The ACLU has been investigating a company called Geofeedia. This week the organization released a document that outlines how the real-time maps of public social media activity were used here in Baltimore.
One example explains how officers tracked online chatter of students who planned to walk out of class and protest at Mondawmin Mall. A Baltimore County police officer is quoted saying “We were able to turn around and alert local police, who intercepted the kids – some of whom had already hijacked a metro bus – and found their backpacks full of rocks, bottles, and fence posts. They planned to do a lot of damage.”
Geofeedia allows users to map out people's posts from Facebook, twitter, Instagram and other social media sites. Specific areas can be searched and monitored, and posts can be filtered by key words.
"When you have a company specifically marketing to law enforcement the ability to search on political themes as a tool of legitimate government surveillance, it raises red flags all over the place," Rocah said.
The ACLU and privacy advocates are concerned the social media surveillance can hurt free speech, and unfairly target minorities.
Both the Baltimore City and County Police Departments pay to use the program, and they see it differently.
"The problem that we have in law enforcement is that the volume of social media activity is so huge that it's almost impossible for us to comprehensively look at relevant posts when we're investigating threats or rumors or trying to plan for some kind of an event," said Elise Armacost with the Baltimore County Police Department.
"Sometimes people are angry, sometimes people want to hurt other people, and when their privacy settings aren't on, and they're letting us know where we are, they're letting us know that they intend to do harm, yes, we want that information, and we use it," Detective Nicole Monroe with the Baltimore City Police Department said.
Baltimore Mayor Stephanie Rawlings-Blake says the surveillance doesn't violate personal privacy because all of the images, geo-location data, and screen names being tracked are available on the public feeds.
"We have a city that is largely too violent and citizens that on a daily basis are asking us to do more to make Baltimore safer, and we'll continue to do that," she said.
ABC2 News reached out to Geofeedia for a statement, but our calls were not returned Wednesday.
Facebook, Twitter and Instagram have all pulled Geofeedia's developer access to their data because the company violated the terms of service. Both the Baltimore City and County Police Departments tell us they're evaluating if they will continue to contract with Geofeedia.