CLEVELAND -- The Cleveland firefighter charged with killing three people over Fourth of July fireworks is challenging the prosecution's claim that the attack was planned, NewsChannel5 reported.

The attorney for Terrance Hough Jr. said his client snapped before shooting into the crowd at his neighbor's home.

"He didn't walk out there with the intent of killing anybody. It just, it happened," John Hildebrand said.

Hough, 35, is charged with three counts of aggravated murder.

Hildebrand also said the defense was investigating medical issues that might be raised on Hough's behalf. Hildebrand wouldn't elaborate, but firefighters and others who work rotating shifts can be more subject to sleep disorders.

According to the National Sleep Foundation, shift workers often don't get enough sleep, which can lead to irritability, impatience, anxiety and depression that can "upset job and family relationships, spoil social activities and cause unnecessary suffering."

Hough, a 12-year fire department veteran, was indicted Tuesday on three counts of aggravated murder and two counts of attempted murder. He faces the possible death penalty if convicted of any of the most serious counts.

The indictment alleged that Hough planned the killings, a key element in death-penalty cases.

Cuyahoga County Prosecutor Bill Mason said firing at victims who had already fallen to the ground wounded showed the attack "was not a mistake, that's a very intentional act." Two victims were shot in the back.

One wounded survivor, Donny Walsh, 23, told The Plain Dealer last month that Hough never complained about the noise and shot without warning.

Hough, who has been jailed without bond, is to be arraigned Friday.

Hildebrand said Hough remains depressed over the matter but his demeanor has improved. The case has been tough on his wife and children, who haven't returned to their home and probably will move out of the neighborhood, Hildebrand said.

Police at the scene said the shootings on the neighbor's driveway apparently were prompted by anger over fireworks and a loud party.

Hough's wife had called police several times between 2003 and 2005 complaining about loud noise, drugs, underage drinking and problems with neighbors, police reports show.