Dustin Brown wanted a secure grip on the two knives he had selected to slaughter the children.

Before leaving his Morton, Illinois, home on the afternoon of October 13, the 19-year-old wrapped each knife's handle carefully with duct tape. He then pulled on a pair of grippy gloves. The one-mile journey to the public library gave Brown one final chance to rehearse the plan he had contemplated for the last two weeks. Five-inch blades jingled together in his backpack all the while.

Hanging over everything, child pornography charges threatened to ruin Brown's life. Despite some rudimentary precautions, his online cache of videos had been unearthed by investigators earlier in the year. Searched, arrested, and eventually expelled from Morton High School, Brown felt he had nothing left to live for. In this lowest of moments, he wanted only to destroy the lives of others before turning his duct-taped knives on himself.

Morton, a 17,000-person village just outside of Peoria along I-74, bills itself as the "pumpkin capital of the world." Its claim to fame lies in its thousands of acres of pumpkin farms, along with an enormous Nestlé plant that cans Libby's puréed pumpkin. Directly behind the Nestlé plant, across the railroad tracks, sits the town's single-story brick library. At 3:25pm, Brown walked inside and sat down at a table. He looked around. A chess club was meeting in the library conference room, and Brown watched the 16 children—some as young as seven—with rising rage. Furious at the legal charges against him, Brown saw a way to exact a twisted form of revenge against children. He opened his backpack and pulled out the knives.

Inside the conference room, 75-year-old instructor James Vernon looked up from a chess board and saw Brown running toward him. Brown held a knife in each hand; as he entered the conference room, he screamed out, "I'm going to kill some people!"

Though Vernon had spent his career in IT at the local Caterpillar plant, he had taken knife-fight training in the Army many decades before. He immediately stepped forward into Brown's path, trying to distract the young man—but also hoping to see which hand he might use to attack. Local newspaper reporter Michael Smothers spoke to Vernon afterward about what happened:

“I tried to settle him down,” [Vernon] said. “I didn’t, but I did deflect his attention” from the children “and calmed him a bit. I asked him if he was from Morton, did he go to high school. I asked what his problem was. He said his life 'sucks.' That’s a quote.” As Vernon spoke, he stepped closer to Brown. “He backed away when I’d get closer.” With a few steps, Vernon put himself between Brown and the room’s door, with the children under the tables behind him. “I gave them the cue to get the heck out of there, and, boy, they did that! Quick, like rabbits,” Vernon said... Vernon watched what Brown did with his knives and learned. “I knew he was right-handed. He was whittling on his left arm” with the one in that hand, “making small cuts. He was trying to scare me, and he did.” But if Brown attacked, “I knew which hand it was coming from.”

The attack came with a sudden slash. Vernon threw up an arm in defense, taking cuts to two arteries in his hand and wrist, before shoving Brown hard toward the tables. Brown landed with his bodyweight pinning his left arm beneath him, rendering the second knife ineffective. Vernon, bleeding profusely, grabbed Brown's right wrist with one hand and punched Brown repeatedly in the right shoulder until the assailant dropped the first knife.

Library staff rushed in to disarm Brown, holding him until police arrived minutes later. According to prosecutors, while Brown was being led out to a waiting ambulance, he told police and paramedics, "I failed my mission to kill everyone."

The violent conclusion to the story was unusual, but the child pornography investigation that set Brown off was not. Increasingly, such investigations aren't simply spurred by agents monitoring file-sharing networks or infiltrating the paranoid world of online communities dedicated to child sex abuse. While those investigations continue, cases today can commonly arise from tips lodged by Internet companies, especially those that provide cloud storage.

And in this case, Brown's case was set in motion by one of the most popular of cloud storage providers around: Dropbox.