I just had the privilege of attending a small conversation session with Edward Snowden and a number of technology and policy leaders at SXSW. He spoke for about an hour on a range of subjects related to his disclosures, possible federal legislation—good and bad—coming down the pike, and specific issues at the intersection of technology and privacy.

And totally unprompted, to my extreme delight, he repeatedly raised the spectre of the trickle down of mass surveillance data to the state and local police. I couldn’t agree more with him that this is a central and largely undiscussed problem.

Here’s what he said, touching on stingray surveillance and obliquely referencing so-called ‘fusion centers’, places where state and local cops obtain and disseminate ‘intelligence’ information, some of it classified.

It’s happening in a dark room, behind closed doors, to some bad guy. [People] want to think it’s about terrorists. [These programs] never made a concrete difference in any [terrorism case] at all.

…

They’ve got everything. The question becomes, Now they’re empowered. They can leak [this stuff]. It does happen at the local level. These capabilities are created. High tech. Super secret. But they inevitably bleed over to law enforcement. When they’re brand new they’re only used in the extremes. But as that transition happens, more and more people get access, they use it in newer and more and more expansive and more abusive ways. How do we counter that? We stop it from happening. The risks are too great. It does give us espionage advantage. But that’s really marginal. Mass surveillance can be really helpful, but it’s not absolutely necessary. We can still target embassies and ambassadors. There are lots of ways in.

The local PD knows where my cellphone is at night. It knows what other cellphones are there with me. That transition from intel to law enforcement is not just in countires like Turkey. SHENANIGANS: We would fly planes over countries collecting all the wireless IDs. Which cellphone works in which building during the day. You can start collating hardware addresses with patterns of life. That same technology was revealed by the WSJ…is being used by the DEA within the United States. As these get cheaper…they’re put on drones that can orbit perpetually, it’s going to become more and more of a problem. DO we want to reorient our societies so that everyone knows who everyone is sleeping with? Or do we want to get back to the point where, rather than try to weave our way through legislation, we can create systemic standards [that allow people to have control.]

On stingrays and other cell site simulator spying, Snowden said that secrecy enables not only warrantless government surveillance, but protects the police power from constitutional scrutiny. In other words, if you don’t know cops used a stingray to lock you up, you can’t challenge the constitutionality of the surveillance during your trial. “People went to prison without the ability to challenge the lawfulness of this collection against them,” Snowden said.

But if we fix the problem of bad law, we still need to deal with oversight and enforcement. “Even if there are laws on the books, if officials believe they can flout those laws [and get away with it, those laws don’t matter],” Snowden warned. And he’s right—from the NSA to the FBI all the way down to our local police departments. Without independent oversight, laws constraining police powers don’t matter much for the people targeted by abusive officers or systems.

Finally, someone in the crowd asked Snowden if, knowing what he knows now, he would leak these documents again.

“Absolutely,” he said. “I lost a lot. I can’t come home and that bothers me a lot. I wish it weren’t the case. But I’ve gained so much. I have the ability to contribute. It gives me a reason to get up in the morning. And that’s something that you can’t get other than having a principle that you believe in very strongly.”