Brendan Dassey could have saved the 25-year-old photographer who showed up at his uncle's junkyard for an assignment, prosecutors said. Instead, the teenager raped her and joined in killing her on Halloween, then burned her body in a barrel.

"A tragedy occurred that did not have to happen," special prosecutor Ken Kratz said Wednesday after Dassey, 17, was found guilty of homicide, sexual assault and the mutilation of a corpse in Teresa Halbach's 2005 death.

Dassey's uncle, Steven Avery, 44, was convicted last month of Halbach's murder.

During the teenager's nine-day trial, jurors watched a videotaped statement in which Dassey described how the young woman was raped and killed. Dassey later recanted, but a jury convicted him.

The case drew national attention because Avery had been released from prison two years before Halbach's murder when DNA testing showed he couldn't have committed a 1985 rape for which he was serving time.

Halbach disappeared after going to the Avery family's auto salvage yard to photograph a minivan Avery's sister was selling through Auto Trader Magazine. Her cousins later found her vehicle in the lot, partially concealed by branches, wood and car parts.

Unlike Avery, who did not testify at either trial, Dassey took the stand in his own defense, saying he had lied when he told of going to Avery's home, seeing Halbach shackled nude in a bed, raping her and helping Avery kill her and burn the body.

He said he made up the story but may have taken some details from a book he read.

"I don't know," he answered repeatedly when asked why he would say such things.

The prosecution argued that evidence such as leg irons and handcuffs in Avery's bedroom and two bullets — one with Halbach's DNA on it — matched what the teen had told investigators.

Investigators found charred fragments of her bones in a pit behind Avery's garage and in a barrel, along with her camera and cell phone.

In closing arguments, special prosecutor Tom Fallon said Dassey accepted his uncle's invitation to rape Halbach because he wanted to know what sex was like. Dassey helped kill her and burn her body to dispose of the evidence of the crimes, the prosecutor said.

But defense attorneys argued there was little that tied Dassey to Halbach's death, other than what they claim was a false confession.

"What we don't see up until this point and have not heard is anything scientific that matches Brendan Dassey, that places Brendan Dassey at Steven Avery's at the date and time of the killing. No DNA. No fingerprints," defense lawyer Mark Fremgen said.

Fremgen said an appeal was likely.

Dassey and Avery both face mandatory life terms on the homicide charge. Avery is set to be sentenced June 1 and Dassey on Aug. 6.

Mike Halbach, Teresa's brother, said his family was relieved the trials were over.

"Hopefully Teresa can now enjoy her time in heaven instead of worrying about us," he said. "We're sending both of them to prison."