Two 16-year-old girls have been charged by prosecutors for plotting a Columbine-style attack to kill their classmates at their school in Highlands Ranch, Denver, Colorado last December.

Brooke Higgins and Sienna Johnson were charged as adults with conspiracy to commit first-degree murder under extreme indifference and conspiracy to commit first-degree murder after deliberation, according to 9News.

The two plotted to kill their classmates at Mountain Vista High School, a public school. The court set the bond at $1 million for each of the suspect.

According to a 7News report, prosecutors said Johnson referred to Higgins in her journal to say that she "found someone who's got what it takes," adding that they would be "unstoppable" and "prove what we are capable of." Johnson also wrote they'd make the school "a living [expletive] nightmare."

Higgins also searched online for places where underage kids could purchase guns and also visited Armslist.com, which is like a Craiglist for firearms.

She also searched "female mass shooter" using her cell phone and wrote in her journal that she wished she could have been part of the Columbine attack.

The two students were arrested on Dec. 12 after the Douglas County sheriff's officers uncovered their alleged plan.

Someone allegedly sent a text message to alert Douglas County about the plan. The tip added that Higgins and Johnson would carry out the attack the following week.

Senior Chief Deputy District Attorney Jason Siers said the fact that the two were charged with the same crimes means that prosecutors believed they were co-conspirators.

"The investigation leads us to believe that there is a connection between the two. Certainly the charge requires an agreement between the two of them in order to charge the case," Siers said.

Mountain Vista High School has about 2,200 students.

Higgins will be back in court on Jan. 21 while Johnson is set to appear on March 30 and 31.