Connecticut State Police Trooper First Class Walter Greene — who contracted cancer after serving as a first responder in wake of the terror attacks on 9/11 — died Thursday after a lengthy battle with the disease.

Greene, 51, lived with his family in West Norwalk and was a first responder after the 9/11 terrorist attack in New York. He contracted a rare form of cancer as a result of exposure to dangerous elements after the attack, according to Gov. Dannel P. Malloy’s office. Malloy ordered that flags across the state be lowered to half-staff to honor Greene.

Greene was part of the state police canine unit that was immediately called to assist New York police in searching for bodies among the rubble of the Twin Towers. Greene and his dog spent several days searching through the rubble looking for survivors. That unit is nationally known for its search and rescue abilities, the Hartford Courant reports.