Last year, your office interviewed about 2,500 possible victims. Do you have a sense of how bad things are in Chicago as opposed to elsewhere?

It’s bad here, but it’s bad everywhere. Technology-wise, kids in parts of our city are getting their own cellphones earlier than some kids in more rural areas. The internet has revolutionized every aspect of daily life: shopping, banking, the access people have to our kids. Predators don’t have to go to a park and lurk. They can violate kids from their own homes, over and over again, with complete anonymity.

What makes these predators so hard to catch?

The training and the licenses and the equipment involved in these investigations are all very costly. You can’t just go into someone’s house and take their laptop and open it up. You’re altering forensic evidence if you don’t do it the right way. It’s like a murder scene with a puddle of blood; an officer would never run in and make footprints in it. And it’s a challenge to have enough evidence to charge someone. I believe Facebook intends to move forward with complete encryption of Messenger. And if Facebook starts to encrypt their data, then that’s millions of investigations for which we will potentially never get the evidence that would lead to prosecution.

What can parents do?

You would never just give your 16-year-old a brand-new car and end it there. You’re going to make sure that they’ve gone to driver’s training, and then once they get the car, you’re going to monitor them. Parents don’t do that with smartphones. We had a case recently of a 10-year-old who was sending naked pictures of herself. This isn’t a teenage issue. I started these types of conversations when my child was 5.

How has working in this field changed you?

Coming over to this specialization, I knew it would be difficult, but I thought, OK, well, I’ve done very difficult things in my career. This isn’t going to be any different. But that’s just not the case. Every single day I’m exposed to this element of society that truly is the underbelly. In past assignments, I would talk to my family: “Let me tell you about this case.” I don’t do that now. I’m completely isolated on a personal level, because these aren’t situations that I want to burden anyone else with. At a block party, if someone says, “What do you do?” I say, “I’m a prosecutor,” and I try to stop there.

When do you think you’ll let your children have cellphones?

I tell them, “Don’t ask me again until high school.”