HIGHLANDS RANCH, Colo. (AP) — Sheriff’s officials say two teen girls have been arrested for investigation of making a credible threat against their suburban Denver high school.

Authorities on Tuesday didn’t reveal details of the threat but did say the charges against the two 16-year-olds could include conspiracy to commit murder.

Douglas County sheriff’s spokeswoman Lori Bronner said authorities were alerted to the plot on Saturday via a text-a-tip program developed for schools.

She said the teens took a substantial step toward completing the act at Mountain Vista High School but declined to elaborate.

Bronner says authorities consider the case contained with no continuing threat.

Mountain Vista was one of many campuses closed in Colorado because of snow.