In December 2023, Ethan Dallas texted his mother, Becca Dallas, that something was weighing on his mind.

“I’m sorry. I feel so bad about myself. I feel like I’m worthless,” the 15-year-old wrote. “Promise you won’t get mad if I tell you?”

Ms. Dallas took Ethan, who was autistic, to a Denny’s near their home in San Diego. There, he made a confession about Roblox, his favorite video game, which he had played since he was 7.

Years earlier, a Roblox player who said he was a child named Nate had messaged Ethan. They became close, playing the online game together every day after school and chatting late into the night. Nate eventually showed Ethan how to disable some of Roblox’s parental controls. Their conversations turned sexual and moved to the messaging app Discord, where Nate demanded that Ethan provide explicit photographs of himself. Ethan complied after Nate threatened to publicly share their conversations.

Ethan began having anger fits, Ms. Dallas said. The outbursts were so intense that in 2022, she and her husband placed him in a residential treatment center for a year. In April 2024, four months after telling his mother about Nate, Ethan killed himself.

This April, Ms. Dallas learned from law enforcement in Florida that Nate was likely Timothy O’Connor, a 37-year-old man. He had been arrested on separate charges of possessing child pornography and transmitting harmful material to minors. Florida law enforcement worked with the National Center for Missing and Exploited Children, which Ms. Dallas had contacted about Ethan’s situation, and connected his case to Mr. O’Connor.