海角大神

For up to 10 hours a day, a Cessna propeller plane circled the city of Baltimore, secretly monitoring about 600,000 people, capturing their movements and transmitting the data to private security analysts.

Operated by a firm called Persistent Surveillance Systems, the small plane circled 8,500 feet above ground snapping wide-angle images of citizens represented as one-pixel dots on computer screens below.

鈥淥ne pixel per person allows me to follow a dot, which usually goes a block or so, jumps into a car and drives off,鈥� says Ross McNutt, whose company assisted Baltimore police in a trial program earlier this year. 鈥淲e follow the people and vehicles to and from crime scenes.鈥�

That program, first reported by in August, has since ended. Police spokesman T.J. Smith says the department last operated planes on Oct. 15, monitoring a major naval event and the Baltimore marathon. Since then, 鈥減olice departments from around the world鈥� have contacted the city to express interest in the aerial program and determine its effectiveness, says Smith, who declined to聽specify which ones.

The program highlights growing interest among police departments in tools that often elicit criticism when made public. An astronautical engineer who trained at the Massachusetts Institute of Technology,聽Mr. McNutt says his company has conducted operations in about a dozen US cities 鈥� including Philadelphia and Los Angeles 鈥� that closely resembled the Baltimore trial.

鈥淣o one wants to be first 鈥� they get yelled and screamed at,鈥� says聽McNutt, who says聽he welcomes public debate around his surveillance technology.聽鈥淚t鈥檚, 鈥極h my God, Big Brother鈥檚 watching me.鈥� Well, I hate to tell you, there鈥檚 cameras all over the place. All we鈥檙e doing is helping make them effective.鈥�

WATCH: Special report on surveillance in Baltimore

More than a thousand cameras聽on stoplights, buildings and poles聽surveil Baltimore passersby throughout the city streets. Since 2005, police have paired privately owned cameras with city ones, weaving together a vast surveillance net in which little remains private.

But its surveillance goes well beyond conventional measures. Baltimore uses technology known as 鈥淪tingrays鈥� 鈥� devices that impersonate cellphone towers to capture and track calls 鈥� license-plate readers, and facial recognition to monitor citizens. In August, three privacy groups filed a Federal Communications Commission (FCC) complaint alleging the city鈥檚 above-average use of Stingrays disproportionately affected minority communities and disrupted cell service.

While conventional surveillance tools聽such as wiretapping and cameras聽have established usage guidelines, these new technologies exist in a sort of 鈥淲ild West,鈥� largely unhindered by regulations and oversight.

McNutt says his technology, which is bound by a strict internal privacy policy even as many of his clients don鈥檛 have one, was adapted from a tool he built for the US Army. In 2006, at the peak of the Iraq war, the Pentagon asked McNutt to help cut down deadly roadside bombs. His solution? Angel Fire, a wide-area aerial surveillance system that could monitor the roads in real-time.

鈥淚t invariably happens that technology developed for military applications gradually percolates out to domestic policing,鈥� says Julian Sanchez, a senior privacy fellow at the libertarian Cato Institute. 鈥淲e talk about police militarization usually thinking about 鈥� SWAT-style gear, but there鈥檚 a parallel phenomenon on the surveillance side.鈥�

But Smith, the Baltimore police聽spokesman, says as criminals adapted to existing technologies, police needed to become more 鈥渃reative.鈥� Since news of the aerial program broke, he says the department has received an 鈥渦nprecedented鈥� number of calls from citizens hoping to solve old crimes. He had not, however, heard a single complaint from 鈥渃ommunities most affected by this violence.鈥�

And there is some indication it may be working. After its bloodiest year ever in 2015, Baltimore鈥檚 homicides have dropped 7 percent, from 311 to 290. Smith said the week when Baltimore鈥檚 surveillance program was revealed, it had only one daytime shooting,聽down from an average of more than five in weeks before. And, he added, the program has led to at least one murder prosecution and helped investigate multiple nonfatal shootings.

鈥淲e have a responsibility as a public safety agency to do everything legally possible to capture the people who committed these crimes,鈥� Smith says. 鈥淧eople who are trying to harm us get more and more creative every day.鈥�

Is surveillance working?

Jay Stanley, a privacy expert at the American Civil Liberties Union, says new technologies such as aerial surveillance have potential on a 鈥渃ase-by-case basis,鈥� but need public debate and oversight. This fall, the ACLU launched legislative efforts in 11 US cities to promote 鈥渃ommunity control over police surveillance鈥� by mandating elected officials 鈥� not police departments 鈥� decide when to adopt new surveillance technology.

鈥淭he primary checks and balances of local democratic decision-making bodies is the power of the purse,鈥� Mr. Stanley says. 鈥淲e鈥檙e seeing that system being short-circuited because police departments are getting outside grants. 鈥� So police departments can get this bag of money dropped in their laps ... and they don鈥檛 have to go to the city council to get permission.鈥�

In addition, Stanley says many new surveillance tools lack strong reporting metrics, making it difficult to determine their effectiveness. McNutt鈥檚 company, for example, has devised ambitious聽goals, such as cutting crime by 30 percent,聽but most remain untestable since his programs operate in secret.

In Baltimore, Smith says his department would wait for an upcoming report to determine if it should continue aerial surveillance.

The report, set for release next month, is being compiled by the Police Foundation,聽a nonprofit that facilitated a private grant from the Laura and John Arnold Foundation to fund the aerial surveillance program. While the Police Foundation declined to share specific details from the report, president Jim Bueermann said the program in Baltimore was 鈥減robably鈥� not set up with a 鈥渞igorous scientific method鈥� and had 鈥渄ata issues.鈥澛�

鈥淎cross the landscape of policing there are very few performance measurements in place,鈥� he says. 鈥淚t just has not historically been something that policymakers have demanded and few police chiefs and sheriffs have spent enough time on trying to understand what works and what doesn鈥檛.鈥�

When asked about the lack of a 鈥渞igorous scientific method鈥� for analyzing the surveillance program, Smith said he had 鈥渘o knowledge of that.鈥�

Quickly evolving technology聽

Across the country, police are utilizing and repurposing existing technology to monitor citizens and fight crime 鈥� without much data to back it up. In Oakland, Calif., for example, police received federal funds to build a Domain Awareness Center capable of analyzing live video in conjunction with license-plate scanners and gunshot detectors. When citizens discovered the center in 2013, they were shocked.

鈥淣ot a single person in my circle knew this project existed,鈥� says Brian Hofer, an Oakland-based privacy advocate. 鈥淗ow has this multimillion dollar surveillance project gone this far with no public scrutiny? You can鈥檛 regulate something if you don鈥檛 even know it exists.鈥�

Left unchecked, the hub would have bolstered police surveillance by merging live video and license plate readers with newer thermal imaging and body movement software. In the future, documents showed, it could have included facial recognition to allow for real-time video analysis.

Mr. Hofer and other privacy advocates successfully scaled back development of the center in 2014 and he now chairs a standing privacy committee in Oakland.

Alvaro Bedoya, executive director of the Center on Privacy and Technology at Georgetown University, says unchecked use of facial recognition 鈥� as proposed in Oakland 鈥� threatens democracy. In a recent report, the center called for greater transparency over enforcement agencies that access photos of more than 117 million Americans often without legislative approval.聽

鈥淒oes it look like America when you walk outside for a protest and you can have your face photographed, scanned, and identified in secret by your government?鈥� Mr. Bedoya says. 鈥淪ecurity and safety is not the end-all be-all of how we run our government. Freedom also has a say in that.鈥�

In the future, Bedoya says, surveillance will shift from devices to people. Law enforcement will聽track immutable characteristics like iris structures, behavioral patterns and voice recognition.

鈥淗istorically, police have tracked your technology 鈥� your car, your phone, your computer,鈥� he says. 鈥淵ou can turn off your phone, you can leave your car at home; you can鈥檛 turn off your face.鈥�

Story by David Fishman and video by Michelle Kim, both students at Northwestern University.聽