(CNN) An investigation into the death of a mentally ill man who was repeatedly tased in his shower by two West Milwaukee police officers has concluded with no charges being filed, Milwaukee County District Attorney John Chisholm said.

The medical examiner said the cause of Adam Trammell's death on May 25, 2017, was "excited delirium" and the manner of death was undetermined, according to the district attorney's report obtained by the Milwaukee Journal-Sentinel newspaper.

"I do not believe there is a sufficient factual or legal basis to believe that either officer's actions were a direct or indirect factor in his death," Chisholm said.

Excited delirium is characterized by agitation, aggression, acute distress, unexpected physical strength and sudden death, according to the US National Library of Medicine.

But a lawyer for Trammell's family said the 22-year-old should not have died.

"He was naked in the bathtub. He had no weapon," attorney Mark Thomsen said. "There is no reason in any situation that a young African-American male suffering from mental illness should be shot [with a Taser] 15-18 times and then die."

He called the police action "unconscionable."

"They should have treated him like he had a mental illness and taken him to the hospital," Thomsen said.

"This is a nightmare. I can't believe this," Larry Trammell said. "I think those people should resign. The D.A. and the chief of that police department."

Naked in the shower

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Trammell suffered from schizophrenia and was bipolar, said the medical examiner's report, according to CNN affiliate WISN

Officers Michael Rohleder and Anthony Munoz went to Trammell's apartment after somebody called 911 to report a naked man in the hallway, the district attorney's report said. The caller said they feared he was having a "psychotic break," the report said.

Body camera video obtained by the Journal-Sentinel showed the officers knocking on the door and breaking it down with a battering ram when nobody answered. The video showed officers walking into the bathroom and speaking to a wet, naked Trammell standing in the shower. They mistakenly call him "Brandon."

Trammell, who was drinking a liquid from a clear plastic jug, stared silently at Officer Munoz when Munoz spoke to him, and used his open hand to push Munoz's forearm when the officer touched him, the report said. At that point, the report said, Munoz realized that the liquid Trammell was drinking was hot water. In the body camera video, an officer says, "You're going to get tased," then a snapping sound is heard and Trammell screams and falls onto his back in the tub.

A Taser, sometimes called a stun gun, shoots barbs attached to wires that stick into a person's body. The person holding the Taser can deliver an electrical shock, which temporarily incapacitates the person who was shot.

Several other jolts of electricity were delivered to Trammell as he struggled with the officers, who handcuffed him and tried to get him out of the tub, the report said. He grabbed onto Munoz's Taser and tried to bite Munoz, the report said.

Realizing the Tasers were not effective and that they could not "gain control of" Trammell on their own, the officers went into the apartment hallway, leaving Trammell inside the apartment until backup arrived, the report said. Several officers began carrying him out of the bathroom by hand, and one officer struck him in the face when he struggled, the report said.

When they reached the hallway, Trammell began vomiting while remaining combative, the report said, and a Milwaukee Fire paramedic administered ketamine to calm Trammell.

His breathing slowed and then stopped, the report said. He was carried to Froedtert Hospital by ambulance and pronounced dead at 6:32 a.m., the report said.

Tased how many times?

Thomsen said Trammell received 15-18 electrical jolts from a smaller number of Taser firings. When the Taser prongs stayed embedded in Trammell's body, multiple jolts could be delivered on the same shot, he said.

West Milwaukee Police Chief Dennis Nasci told CNN the Taser made contact only five or six times.

The district attorney's report said Tasers were "cycled or discharged 15 times," with an electrical charge delivered in at least half the Taser deployments. Some of the probes may have dislodged in the struggle, the report said.

The only times he was clearly tased "result in Mr. Trammell screaming in pain, but did not result in compliance," the report said.

'Most reasonable restraint'

The report quoted Munoz and Rohleder saying they used the Tasers because they thought they were dealing with a medical emergency that would require a patient to be calm to receive treatment.

The district attorney concluded the officers did not use the Tasers abusively because that was "the only reasonable restraint available to the officers that offered a middle-ground between doing nothing and escalating force. ..."

There was no criminal culpability because there's "no evidence the officers intended to harm Trammell," the report said.

"Cpl. Rohleder and Officer Munoz responded to a medical emergency under complex circumstances that required them to attempt restraint," the report concluded. "Under all the circumstances, I find their actions did not violate the law and will close this review."

Nasci, the West Milwaukee chief, told CNN that both officers are still on patrol.

"We're happy that the D.A. was able to get this done," he said of the report. "It's an unfortunate event. It's unfortunate, you hate to have any family go through that."

Thomsen told WISN he thinks Trammell was "essentially tortured to death. That should not happen to the mentally ill in our community."

Trammell's family is devastated by the death, he said.

"They've seen the video and they weep every time they see it," he told WISN.