She was an undercover cop who called herself “Missy.” When I first met her four years ago, I couldn’t have known that the small-framed woman with spiky brown hair and intense eyes was anything but a fellow activist showing up for a protest in Washington, D.C.

I certainly didn’t know she was actually Nicole Rizzi, an undercover cop ordered to secretly spy on peaceful protesters, violate our freedom of speech and assembly, and disregard our right to privacy.

Sure, I thought something was odd about her. She stared just a little too long. Her irreverent sense of humor made the hair stand up on the backs of a lot of necks. Her favorite t-shirt read “OBEY” and it wasn’t clear that she wore it for the irony.

A “selfie” photo of Nicole Rizzi, a.k.a. “Missy,” posted to her own Twitter account on March 21, 2013. She posed as a protester at a Keystone XL pipeline demonstration that day.

When I looked at her rippling arm muscles, I wondered whether they came from workouts at some spy academy or a downtown yoga studio.

So sure, I did suspect from the start that she could be an FBI agent, a police officer, or something else. But if you start being suspicious of newcomers, every honest newbie will look like an infiltrator. I kept my paranoia mostly to myself.

It turns out that hanging out in bars every so often can make good things happen. One late night in November 2012, I was in a bar in D.C.’s bustling U Street neighborhood when a friend of a friend from out of town pulled up a Twitter account on her phone, @snufftastic. It belonged to a humorous motorcycle enthusiast and cop. She lives in the area, she said, asking if my friend and I knew her.

“I absolutely know who that is,” I said.

The Twitter account was shocking. There was “Missy” tweeting about he daily grind of working for the District of Columbia’s Metropolitan Police Department. There were photos of her at the shooting range and a photo of her giant walkie-talkie. There were tweets about “the academy” and “the new morgue.”

There was a comment about her working during Barack Obama’s presidential inauguration on “ninja assignment,” and a remark that reading Miranda rights isn’t actually required.

A “snuff007″ Tumblr account attached to her fan fiction site had a comment about her not dressing for “plainclothes assignments” but wearing “what would blend in.”

Spying on protesters is the worst violation of our freedom. It not only violates the freedom of speech, freedom of assembly, and right to privacy of the people who are being spied upon, it makes us crazed and paranoid.

One person who turns out to be an infiltrator can keep us pointing fingers at each other for years. It makes us distrustful of people we don’t know, instead of finding safe ways to welcome newcomers and building vibrant social movements.

Distrust can mean slow death for a group of any kind.

I started warning my friends that “Missy” was a cop. Most weren’t surprised. But could she be a police officer attending protests in her free time, I wondered? After all, like all of us, police have the right to protest. Then I noticed a Tweet that complained of working outdoors on March 21, when I saw her at a march to protest the Keystone XL pipeline.

On April 20, she complained again of working outdoors, and she showed up at a protest outside the World Bank.

That’s when I arranged a meeting with Jeffrey Light, a lawyer who works on police misconduct issues. With the help of Sean Canavan and the National Lawyers Guild, and the involvement of United Students Against Sweatshops, Light and Canavan dug up information on “Missy’s” true identity. They concluded that she was an officer named Nicole Rizzi who joined the D.C. police force in 2003.

In early August, we filed a suit against the District of Columbia seeking an injunction to stop this police spying and to find out more about its infiltration program.

It’s the first case that promises to prove that the police systematically spies on activists in our nation’s capital.

Now that we’ve blown officer Nicole Rizzi’s cover, “Missy” won’t be snooping on any more protests. But our First Amendment rights will continue to be thrown under the bus unless we fight to defend them.