When Sara Haynes heard about the shooting at STEM High School in Highlands Ranch, Colorado on Tuesday, she prayed. A Catholic school teacher in Denver until just recently, she knew some of her former students were now high schoolers at STEM.

When Haynes learned that Kendrick Castillo, a former student of hers, was the lone casualty in the May 7 shooting, she cried immediately.

Then she reached out to the other students who had been in the same 7th and 8th grade math and religion classes at Notre Dame Catholic School as Castillo. Details of Kendrick’s death were not yet public, but her students guessed Castillo had died trying to protect others, Haynes said.