Researchers at a Boston University laboratory discovered that Robert Card - the Army Reservist responsible for Maine's deadliest mass shooting - had sustained extreme brain damage that was likely the result of his exposure to grenade blasts.

Last October, Card killed 18 people and wounded 13 others in Lewiston, Maine when he went on a shooting spree at a bowling alley and a nearby restaurant. After a two-day manhunt, Card was found dead from a self-inflicted gunshot wound.

In the months before the shooting, Card's family and colleagues had become increasingly concerned about his mental health. He was experiencing delusions, lost a large amount of weight and began acting erratically. Several people reported concerns about Card's behavior to the police and his family members made unsuccessful attempts to remove firearms from his possession.

Card's brain was sent to the Boston University CTE Center - which is renowned for its research into chronic traumatic encephalopathy, a condition often found in athletes who experienced head trauma playing contact sports.

While Card did not suffer from CTE, he did patterns of brain damage comparable to other veterans exposed to weapons blasts, the New York Times reported.

Card served as a grenade instructor for the Army for eight years - exposing him to thousands of explosions that literally shook his skull. His brain's white matter had "moderately severe" damage, while the axons that transmit information through the brain were destroyed.

"I'm seeing cables that have lost their protective wrapping, cables that are just missing, cables that are inflamed and sick, cables that are essentially filled with cellular garbage bags," Boston University neurologist Dr. Lee Goldstein told the New York Times. 

"These cables control how one part of the brain communicates with another. If they are damaged, you can't function right."

The Army received similar warnings about grenade blasts causing brain damage in the past, with one study revealing that some grenade instructors have elevated levels of beta-amyloid - a protein usually found in Alzheimer's patients.

"In a young brain you should see no amyloid. None. Zero," University of Missouri neuroradiologist Dr. Carlos Leiva-Salinas told the New York Times.

In response to the Boston University revelation, the Army said it was "committed to understanding, mitigating, accurately diagnosing and promptly treating blast overpressure and its effects in all forms."

For Card's family, this new information is allowing them to heal and better understand what went wrong.

"It allowed me to forgive him," Card's sister told the New York Times. "Maybe we can use what happened to help other people."