The service is planned just a few hours before the two suspects are due back in court. Castillo along with classmates Brendan Bialy and Joshua Jones are credited with helping minimize the bloodshed by charging at one of the suspects in a classroom.
According to Bialy, Castillo sprang into action against the shooter "and immediately was on top of him with complete disregard for his own safety." Jones said he was shot twice in the leg during the ordeal. Bialy said he was able to take the gunman's weapon.
Castillo was a member of the school's robotics club who loved to tinker. He worked part-time at a manufacturing company that had offered him a job after an internship because he was such a standout employee.
Friends say he had an infectious smile, a gentle sense of humor and was excited to help people. Eight students were wounded in the STEM School Highlands Ranch shooting and the last hospitalized one was released on Sunday.
Investigators have said Devon Erickson, 18, and 16-year-old Alec McKinney, who is listed in court records as Maya, walked into their school with handguns and opened fire. Investigators have offered no motive and refused to discuss how the students obtained the weapons.
They were arrested Tuesday and are being held on suspicion of murder and attempted murder. Commissioners in the county took the first step Monday toward committing $10 million to pay for security upgrades and mental health services at all public schools in the area. A vote is scheduled for May 28; commissioners said they want to talk with experts, residents and students about how to use the money before that meeting.
Commissioners said the one-time payment would come from reserve savings and higher income from property values. The Douglas County School District received a $1.5 million grant from the Colorado Department of Public Safety in February under a program to upgrade security in school buildings and vehicles and train school personnel. District spokeswoman Paula Hans said Douglas County schools would use the money to update the school communications system, including replacing radios. It was one of 95 grants to schools or school districts totaling more than $29 million.