The former employee’s computer searches took place on this employee’s workplace computer. On that computer, the employee searched the terms “pressure cooker bombs” and “backpacks.”
So it wasn't Google, but it was because of searching for pressure cookers; it wasn't posting images of firecrackers on facebook, but it was a tip-off based on (private) surveillance.
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and now we even know why: https://news.ycombinator.com/item?id=6144198
The former employee’s computer searches took place on this employee’s workplace computer. On that computer, the employee searched the terms “pressure cooker bombs” and “backpacks.”
So it wasn't Google, but it was because of searching for pressure cookers; it wasn't posting images of firecrackers on facebook, but it was a tip-off based on (private) surveillance.