BARTOW, Fla. (WFLA) – The Brandon man and former sharpshooter with the U.S. Marines accused of killing four members of a North Lakeland family he did not know may use an insanity defense when he stands trial on four counts of first-degree murder, according to court filings.

An attorney for Bryan Riley filed the intent to rely on a defense of insanity last week after being granted several extensions by the judge.

The document from his attorney shows Riley suffered from a “mental infirmity, disease or defect” at the time of the September shooting.

Because of the condition, which is redacted, “he did not know what he was doing or its consequences; or although he knew what he was doing and its consequences, he did not know that what he was doing was wrong,” his attorney wrote.

The defense listed Dr. Valerie McClain, of Tampa, as an expert witness.

Prosecutors are seeking the death penalty.

Polk County Sheriff Grady Judd announced on Sept. 5 that Riley, a former sharpshooter with the U.S. Marines, allegedly shot and killed four complete strangers in their home, including a baby.

Judd also said Riley injured an 11-year-old girl in the shooting, who told deputies she survived by playing dead until she was rescued.