One of two 16-year-old girls accused of plotting to kill classmates and staff at their Colorado high school last month was formally charged as an adult on Tuesday with conspiracy to commit first-degree murder, prosecutors said.
Sienna Johnson appeared in Douglas County Court to face allegations that she and another girl planned to attack Mountain Vista High School in the Denver suburb of Highlands Ranch, said District Attorney George Brauchler.
Brauchler told Reuters he decided to charge Johnson as an adult based on evidence seized by police, including a journal in which he said the girl drew a map of the school, made detailed notes about where people congregated and tracked the movements of security personnel.