LINCOLN, Neb. (Reuters) - Two former Nebraska police officers will be charged with assault in connection with the June 5 death of a mentally ill Oklahoma man the officers detained, a Nebraska state prosecutor said on Wednesday.

Zachary Bearheels, 29, died after the officers punched and shocked him with a Taser stun gun more than a dozen times while trying to detain him in Omaha, Douglas County Attorney Don Kleine said.

Former Omaha police officer Scotty Payne will be charged with felony second-degree assault and former officer Ryan McClarty with misdemeanor third-degree assault, Kleine said. Both were fired after the incident.

Payne and McClarty could not be reached for comment. Matt Saathoff, Payne’s lawyer, and Joseph Naatz, McClarty’s lawyer, did immediately return calls seeking comment.

Payne faces up to 20 years in prison if convicted. McClarty faces up to a year.

Family members said Bearheels, a member of the Rosebud Sioux of South Dakota, suffered from bipolar disorder and schizophrenia, according to local media. He was taking a bus from South Dakota to Oklahoma when the driver kicked him off in Omaha, police said.

Police were called after Bearheels began behaving erratically in midtown Omaha, licking the windows of a store and dancing in front of another, according to police and local media reports.

The evidence did not show that the officers meant to kill Bearheels, Kleine said.

“They are capable of making serious mistakes in their encounters with citizens,” Kleine said of the officers.

He added that Bearheels had not committed a crime. “He was simply a human being, suffering from a severe mental illness that was quite obvious to anyone who was in contact with him,” Kleine said.

Police dashboard video showed Bearheels was handcuffed, dragged by his hair, shocked and punched repeatedly, Kleine said.

An autopsy listed the cause of death as “excited delirium.” Kleine said no alcohol or drugs were found in Bearheels’ system.

State law requires a grand jury to review cases involving the death of people in police custody. Kleine said he decided to file charges before the grand jury acted.