Whistle-blower Edward Snowden spoke out against the American government’s ongoing privacy violations Monday, saying the National Security Agency's post-9/11 strategy of collecting private information from Americans has done little to protect us from terrorism.

In one case, broad policies and programs for data collection and surveillance may have even obscured or distracted officials from specific targets. Before the Boston Marathon bombing, “the FBI was tipped off about [the Tsarnaev brothers]. They only performed a cursory investigation because of resource constraints,” the former federal security expert said. Last year, he disclosed a cache of documents that revealed a pattern of domestic surveillance.

Snowden spoke to an audience at Harvard via webcam during an interview with Lawrence Lessig, a lawyer, Internet activist, and professor at the university.

“The reality is, we knew who these guys were. We knew they were associated with extremism in advance of the attacks, but we didn’t follow up. We didn’t really watch these guys,” Snowden said.

Wearing a black suit and seated against a dark background, the exiled system analyst again laid out the legal, policy, privacy, and law enforcement abuses implicit in the American government’s practice of widespread metadata collection. Most recently, these campaigns against government surveillance have been the subject of Laura Poitras’ new documentary, CITIZENFOUR (which being distributed theatrically by Radius, in association with Participant—TakePart's parent company—and HBO Documentary Films), and explored in several public discussions with Snowden.

“What really alarmed me during my time at the NSA and the CIA was that we had pivoted. We had changed from focusing on traditional methods of surveillance” and instead invested in large-scale data collection, Snowden said.

According to Snowden, the problem is not simply that the NSA database is “a violation of our natural rights.” Even if the government were just collecting this data, not searching it without warrants, the information hasn’t served its alleged purpose of detecting criminal activity.

Snowden isn’t the first person to point this out. In January, the Privacy and Civil Liberties Oversight Board, an independent group created by Congress after 9/11, released a report that found only one instance in seven years of the NSA telephone metadata surveillance program leading to a legitimate tip on a terrorist suspect. Members had full access to this classified information and were “incentivized to exonerate these programs,” Snowden said.

“We miss attacks. We miss leads, and investigations fail because when the government is doing what it calls a ‘collect it all’ investigation, we’re not seeing anything with specificity. It’s impossible to keep an eye on all your targets when you’re constantly dumping more hay on top of them,” Snowden said.

“We have finite resources, and the question is, should we be spending $10 billion dollars a year on mass surveillance programs at the NSA to the extent that we no longer have effective means of traditional targeted surveillance?”

That the collection of phone metadata distracts from more effective forms of law enforcement wasn’t the only argument Snowden made against the program. He also disagreed when Lessig asked him about a suggestion, first proposed by CIA whistle-blower William Binney, that the data be collected but encrypted and accessible only with proper authorization from the courts.

It’s not enough to have more limitations on how this data can be used, Snowden said. Something this massive and powerful will always be a “database of ruin,” and if the government were collecting everything from everyone, the “temptation to access that information, to use it in new ways, to respond to new threats is simply too great to be ignored,” said Snowden.