(CNN) The night before Alec McKinney allegedly opened fire at a Colorado high school, leaving one dead, he sent a Snapchat message to Devon Erickson outlining his plans, authorities said.

In the message, McKinney allegedly told him not to come to school. "Please don't," Erickson responded, according to a preliminary hearing.

Following the shooting, Erickson told investigators that McKinney made him do it and tasked him with guarding an exit and telling everyone not to move. He said he only fired one shot and surrendered the weapon to the three boys who rushed him, among them Castillo.

But one of the people who rushed him, Brendan Bialy, told investigators that Erickson pointed the guns at the heads of those who rushed him and did not willfully give up his gun, according to Douglas County Sheriff lead investigator Brian Pereira.

Read More