Mendoza-Chaparro's capital offense: stealing a bong, a pipe and other items as he smoked marijuana a few days before Christmas with the people accused of killing him.
Devin Katzfey, 20, Branden Katzfey, 19 and Sarah Zakzesky, 20, are all charged with murder, according to prosecutors. They are still being held in Milwaukee County Jail. It was unclear whether they had hired lawyers.
The victim's mother, Iris Chaparro, told Milwaukee Fox-affiliate WITI that this was going to be her first Christmas with her son in a half-decade because they had lived in separate states for five years.
Instead, police told her that he had been killed.
"It was horrible. They showed me his photo and I couldn't even go to the morgue to identify him," she said.
Investigators pieced together what happened from interviews with Zakzesky and Branden Katzfey - and from Mendoza-Chaparro's Snapchat account.
They identified the younger Katzfey brother as the primary aggressor.
According to the criminal complaint, they were all getting high at Zakzesky's apartment in west Milwaukee. She later told police that she was in and out of consciousness. The first time she woke up, she had sex with Branden Katzfey, the complaint says. She noticed Mendoza-Chaparro asleep on the living room floor.
The second time, Devin Katzfey was shaking her awake. Mendoza-Chaparro was trying to steal, he said. The brothers had seen the drug paraphernalia in his coat.
Enraged at Mendoza-Chaparro's attempt to steal, Devin Katzfey dragged him into the kitchen by his feet. Then the beating began.
Mendoza-Chaparro said that he hadn't stolen anything and begged his assailants to stop. In all, he was punched and kicked about 25 times, until he was unconscious. Then he was beaten some more, the complaint says.
Zakzesky told investigators that the victim "didn't even [have] a chance to raise his fists and fight man to man," according to the complaint.
The victim was already badly injured when Devin Katzfey reached for his phone and logged on to his Snapchat account, according to the documents.
Then Zakzesky wanted the injured man out of her apartment.
"She kept telling Devin Katzfey that they need to take the victim to the hospital but he said no," the criminal complaint says.
They drove him to the alley, the complaint says, and "Devin Katzfey was holding on to the victim as they got out of the car and . . . the victim then fell over in a snowbank by garbage cans."
According to the complaint, Zakzesky told investigators that the unconscious man couldn't stand or sit up on his own.
"She . . . agreed that it was cold enough that someone could freeze to death," the complaint says. "When asked what she thought would happen when they left him there, she said she did not know."
Police found Mendoza-Chaparro in the alley on Dec. 19, wearing a sweatshirt and jeans, which were pulled down. There were signs he had been beaten on his neck and head. It was 14 degrees.
