The Palm Beach County State Attorney declined to charge Michael D'Avanzo for the July crash that injured 18-year-old Farrah Fox.
Investigators say the Palm Beach County deputy was driving 53 mph (85 kph) in a 25 mph (40 kph) when his pickup ran the stop sign and smashed into a truck carrying Fox. The University of Central Florida aeronautics engineering student was comatose for a month and remains in rehabilitation.
Prosecutors said Thursday the stop sign was blocked by a low-hanging tree and drivers traveling at or above the speed limit would not have seen it. D'Avanzo remains on duty. Fox's family declined comment.
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