A man pleaded guilty to involuntary manslaughter Thursday in the case of a Casper man who died six days after being punched at an Evansville bar.

The brother of the victim, however, called the sentence "outrageous" and said family members did not want prosecutors to make the plea deal.

Ivall Sparks, 42, told Natrona County District Judge Scott Skavdahl that he punched Mark Bretz after Bretz "said some pretty derogatory statements about my sister." The blow, he acknowledged, ultimately resulted in Bretz's death.

The punch caused serious damage to Bretz's left eye, and he died following complications during surgery.

Under the terms of a plea agreement with the District Attorney's Office, Sparks would serve three to five years in prison, with credit for time he's served since his January arrest. He will be formally sentenced in the next few months.

In Wyoming, the maximum penalty for manslaughter is 20 years in prison.

"It's a joke," Bretz's brother, Michael Fletcher, said in a phone interview.

Fletcher repeatedly criticized prosecutors and insisted Sparks will be a threat to the community when he is released.

"He walked up and punched an unarmed man from the side," he said. "It's murder."

During his short court hearing, Sparks recalled going with his sister to Butch's Bar in Evansville on Jan. 26. While there, a man approached his niece and pursued her. Sparks told the man, apparently Bretz, to leave her alone.

Later, when the group was waiting for a cab, Bretz made the derogatory statements about Sparks' sister, prompting the punch, Sparks told the court.

Bretz, a 50-year-old widower, told an Evansville police officer that morning he had been hit from behind and couldn't see out of his left eye.

After being struck, Bretz took a cab to Wyoming Medical Center, where a doctor determined his cornea was torn and his retina and lens were missing. He was flown to Colorado later that day.

The injury may not have been life threatening, but surgery was required due to the risk of infection from an open wound on the eye, Natrona County's chief deputy coroner testified during an earlier court hearing.

Bretz experienced bronchial spasms - a condition similar to a severe asthma attack - during the operation and he never regained consciousness. He died on Feb. 1.

Before Bretz died, Sparks pleaded guilty to misdemeanor assault and received a 90-day jail sentence. Sparks was still serving that sentence when District Attorney Michael Blonigen in April charged him with manslaughter.

Sparks remains held at Natrona County Detention Center in lieu of $75,000 bond. At the hearing Wednesday, Skavdahl denied Sparks' request for a two-day furlough to get his affairs in order before sentencing.

Reach crime reporter Joshua Wolfson at (307) 266-0582 or at josh.wolfson@trib.com.