MADISON, Wis. (AP) - A former Wisconsin sheriff's deputy with Lou Gehrig's disease has been found not legally responsible in the killing of his wife and sister-in-law.

Forty-year-old Andrew Steele pleaded not guilty by reason of mental disease to two counts of first-degree intentional homicide in the Aug. 22 shooting deaths of his 39-year-old wife, Ashlee Steele, and her sister, 38-year-old Kacee Tollefsbol of Lake Elmo, Minnesota.

Defense attorneys argued that the disease damaged Steele's brain, making him not criminally responsible for the deaths. Prosecutors believed Steele planned the killings.

Lou Gehrig's disease, also called amyotrophic lateral sclerosis, or ALS, attacks motor neurons, cells that control muscles.

A jury deliberated for about 10 hours until all but two of the 12 agreed the verdict early Thursday.