“Do you have a copy of the letter,” Captain Oleg Kulikov asked me.

He looked excited as he watched my face for any reaction. I had just told the Russian intelligence officer that I had been accepted into the United States Navy’s Reserve Intelligence program, and would soon be an intelligence officer.

Months before that, I had handed Oleg copies of various paperwork about both the program and my application but now he wanted more—he wanted to bring back more solid evidence for his superiors documenting the importance of the man he had recruited to spy for Russia. It was one of our many conversations that relied on face-to-face meetings, that allowed me to fool the veteran Russian spy into believing that he was recruiting me, while in fact I was an FBI operational asset.

It’s no surprise that Russia is actively involved in collecting intelligence on the United States and running operations to undermine America. It is a craft Russia has honed and carried out since the fledgling days of the Cold War, and one that special counsel Robert Mueller’s indictment of 13 Russians, with more reportedly coming, re-enforces is still very much active.

While Mueller’s indictment doesn’t mention the Russian government, it presents methods—such as sending covert agents to operate clandestinely in the United States—that are hallmarks of their intelligence services. Russian intelligence officers arrive in the United States, often posing as diplomats, in what is known as “non-official cover.” As Mueller’s indictment puts it, they come “for the purpose of collecting intelligence to inform Defendants’ operations.”

From my own experience working as a double-agent against Russian intelligence from 2005 to 2009, I know that they collect that intelligence by targeting and recruiting Americans to serve as operational assets.

In the digital age, a common question is why the need to recruit spies? Couldn’t spy services simply collect intelligence from afar? Why risk sending Russians to the United States?

As I learned from my years speaking with Russian intelligence, they are distrustful if not paranoid. As such, I found that the Russians sought to temper their suspicions by understanding the source that is providing them with intelligence—something that requires face-to-face meetings. It is why, for example, in spite of my repeated offers to provide intelligence files over email or other ways that did not require us to meet in person, my handlers steadfastly refused and insisted on meeting to speak with me. These meetings, I learned, were critical in evaluating me. If they didn’t trust me, then they couldn’t trust the intelligence I was passing them. Oh the other hand, if they could validate me and trust me as a source then that trust was extended to the intelligence I provided them.

There was another reason for relying on trusted assets for intelligence: protecting the information that Russia sought. The paranoia of Russian intelligence extended to the belief that they were under constant surveillance by the FBI—a notion that gains credibility in the detailed description of emails and conversations released in Mueller’s most recent indictment.

The value of intelligence collected by Russian intelligence officers was severely diminished if the FBI discovered that Russia had collected it, which is why they chose to have me collect intelligence instead of trying to do so themselves. And in an era of endless and potentially everlasting digital breadcrumbs, it was far better to let an America source collect intelligence and hand it over then risk compromise and detection by doing it themselves.

That same paranoia, I found, made the Russians highly selective in who they chose to recruit. Showing up with a juicy piece of classified intelligence was not enough. They wanted to understand why somebody would be willing to spy for them. The answer to that question was as important, if not more so, than the intelligence an asset could provide.

It was not enough that I was a young man intent on joining the United States Navy as an intelligence officer, my Russian case officer had to believe that I wanted to spy for Russia. This meant creating a persona that would meet the Russian profile of a spy. While I couldn’t change my name or where I lived or went to college, I could invent a caricature of a person I believed the Russians were looking for. So I played the part of a young arrogant man obsessed with money who saw service in the Navy singularly as a way to access information he could sell Russia to enrich himself. It was a profile the Russians understood and accepted, and ultimately the reason they allowed me into their network of spies.

With the news that Jared Kushner’s Top Secret clearance had been “downgraded,” I breathed a huge sigh of relief. I am sure that Russia continues to recruit Americans to support its intelligence operations, and continue to have a similar profile of the type of person that is susceptible to such overtures—someone who is willing to sell for profit access and information from the office they hold.

There is no longer much question that Russia recruited Americans to help in their attack on the 2016 elections. The question, rather, is who. It is a question I am sure Robert Mueller is seeking to answer.

Naveed Jamali is the author of How to Catch a Russian Spy.