He urged those in attendance to be more like his son and put love and compassion for others first.
Brauchler said he spoke with Castillo's parents at the hearing.
All of the wounded students have been released from hospitals. The two schools are separated by about 7 miles (11 kilometers) south of Denver.
About a dozen students were injured and one 18-year-old, Kendrick Castillo, was killed after charging at one of the suspect shooters and disarming them.
Robots were lined up outside Cherry Hills Community Church in Highlands Ranch as people entered in recognition of 18-year-old Castillo's love of robotics.
Castillo's parents also attended the hearing.
Castillo was a Jeep enthusiast, according to his family.
A kayak was on the stage along with a photo of a Jeep and two sports jackets. "Let's show Kendrick's family the love from our Jeep community to them", the post said.
Gov. Jared Polis has declared Wednesday Kendrick Castillo Day in Colorado, writing on Twitter that his bravery wouldn't be forgotten.
Two classmates, Joshua Jones and Brendan Bialy, helped disarm the gunman, they both told ABC News. Brauchler said that discovery evidence prosecutors now have in their possession would be turned over to Erickson's lawyers later Wednesday. A law enforcement official told The Associated Press last week that the guard, a former Marine who has not been named, fired his weapon during the shooting. The official did not address whether anyone was hit.
Investigators are also probing whether a a private security guard at the school, Shamson Sundara, mistakenly fired at least one shot at a Douglas County Sheriff's deputy and whether he wounded a student.
The guard hasn't been identified by authorities.
McKinney appeared in court after Erickson. McKinney is now held at a juvenile facility and will remain there, regardless of the adult charges. McKinney's attorney, Ara Ohanian, said he would seek to move McKinney's case back to juvenile court. It's not clear how soon that could happen. An armed security guard responded to last week's shooting.
A memorial service for the student killed, 18-year-old Kendrick Castillo, is scheduled for Wednesday afternoon.
One of two teens charged in the deadly attack on a suburban Denver school has appeared in court after being charged with multiple counts of murder, theft and arson in the attack.
Devon Erickson appears in court at the Douglas County Courthouse, in Castle Rock, Colo., on May 15, 2019.
Erickson looked toward the judge while attorneys discussed the case.
The judge denied bond for both suspects.
Thousands of people gathered Wednesday in Colorado to honor the life of Kendrick Castillo - the courageous high school student who was killed while attempting to stop last week's STEM school shooting.
While court documents are sealed, the names of charges against the gunmen were listed in electronic court records without any more details.
Classmates from STEM School Highlands Ranch say Kendrick sacrificed his life by jumping on one of the shooters to stop him from doing any more harm. Cops say he rushed one of the two suspects during their rampage to subdue them.