Hochhalter was found in her home in suburban Denver on Sunday. Her family suspects she died of natural causes stemming from her injuries in the 1999 shooting in which 12 students and a teacher were killed.

The investigation into how she died has been transferred to the office that conducted the autopsies of those killed at Columbine, the coroner’s office for Adams and Broomfield counties said.

Hochhalter in 2016 wrote a letter to one of the gunmen’s mother saying, “Bitterness is like swallowing a poison pill,” and offering her forgiveness. Attending a vigil on the tragedy’s 25th anniversary last year — after skipping a similar event five years earlier — she said she was flooded with happy memories from her childhood and wanted those killed remembered for how they lived, not how they died.