Luigi Mangione, the suspect in last week’s murder of UnitedHealthcare CEO Brian Thompson, appears to have suffered a spinal condition that gave him crippling back pain for years, possibly contributing to a resentment of the U.S. healthcare system.

Mangione, 26, has been charged with murdering Thompson in New York City and is expected to plead not guilty. Authorities said they found a three-page handwritten document on Mangione that detailed disdain for the U.S. healthcare system.