Story highlights Police say some of the teens are juveniles but will be prosecuted as adults

The plot was discovered when another student talked to school administrators, police say

(CNN) The teenagers would get together before school and at lunch to talk about a group project: the murder of a classmate, said police in Tucson, Arizona.

But the plot fell apart when another teenager informed on them, police said.

Photos: 5 Tuscon teens charged with planning schoolmate's murder Photos: 5 Tuscon teens charged with planning schoolmate's murder Anastasia Lakin – Anastasia Lakin. Hide Caption 1 of 5 Photos: 5 Tuscon teens charged with planning schoolmate's murder Andrew Totten – Andrew Totten. Hide Caption 2 of 5 Photos: 5 Tuscon teens charged with planning schoolmate's murder Christopher Gibson – Christopher Gibson. Hide Caption 3 of 5 Photos: 5 Tuscon teens charged with planning schoolmate's murder Gabriel Quiroga – Gabriel Quiroga. Hide Caption 4 of 5 Photos: 5 Tuscon teens charged with planning schoolmate's murder Jessica Good – Jessica Good. Hide Caption 5 of 5

The five students at Flowing Wells High were charged with conspiracy to commit murder in the first degree, said police spokesman Sgt. Pete Dugan.

One of the students is 18. The others are juveniles -- two 17-year-old girls and two 15-year-old boys -- but will be prosecuted as adults, Dugan said.

School administrators called police Wednesday when a different student came forward to describe the plan and say that someone had brought a knife to campus, Dugan said.