(CBS NEWS) The new Netflix series "Making a Murderer" is raising questions about the high-profile Wisconsin murder case of Teresa Halbach.

The series focuses on Steven Avery, who has a lengthy rap sheet but spent 18 years in prison for a rape he didn't commit. He was finally exonerated in 2003 by DNA evidence, reports CBS News correspondent Michelle Miller.

Just two years later, Avery was back behind bars -- this time, accused of murder.

When it became clear he was the suspect in Halbach's death, Avery claimed he was being set up.

"So you're telling me somebody planted the body?" an investigator asked him in a interrogation video.

"I didn't do it," Avery said.

"Who did it?"

"I don't know," Avery responded.

Halbach's car, with Avery's blood in it, was discovered in the Avery family's salvage yard. The 25-year-old's cremated remains were just steps away from his trailer.

Avery's teenage nephew, Brendan Dassey, even confessed to being an accomplice.

"I'm just going to come out and ask you. Who shot her in the head?" an investigator asked in an interrogation video.

"He did," Dassey said.

"Why didn't you tell us that?"

"Because I couldn't think of it," Dassey said.

Avery's supporters said police manipulated a frightened boy with a learning disability. Dassey later recanted to his mother.

"Did you? Huh?" the mom asked.

"Not really," Dassey said.

"What do you mean, not really?" she asked.

"They got into my head," Dassey responded.

Halbach was raped and murdered in 2005 - one year after Avery filed a $36 million civil lawsuit for his wrongful conviction in a 1985 rape case. That suit had embarrassed several law enforcement officials in Manitowoc County, exposing possible misconduct.

Two officers from that case also worked the Halbach investigation and helped find her car keys inside Avery's bedroom. Investigators were in the salvage yard for eight days looking for clues.

"I didn't see them plant evidence with my own two eyes. I didn't see it. But do I understand how human beings might be tempted to plant evidence? ... I don't have any difficulty understanding those human emotions at all," Avery's defense lawyer Dean Strang said.

Avery was convicted in 2007 for the Halbach murder and sentenced to life in prison.

Filmmakers Laura Ricciardi and Moira Demos spent 10 years working on "Making a Murderer."

"We were very thorough, and in our opinion, very accurate and very fair," Ricciardi said.

Former Calumet County district attorney Ken Kratz told CBS News the Netflix series leaves out key DNA and other evidence, including cell phone records showing Avery lured Halbach to the salvage yard.

Kratz, the special prosecutor appointed to the case, said the suggestion investigators framed Avery was "irresponsible, and inconsistent with a consideration of all the evidence presented."

The filmmakers said their goal was to document Avery's case as it unfolded in its entirety.

"Our question going in was never about guilt or innocence or about trying to solve this crime. It was really an exploration into the system," Demos said.

Halbach's family did not respond to our request for comment, but before the series was released, they issued a statement saying they were saddened people were creating entertainment and trying to profit from their loss. CBS News also reached out to other police and prosecutors mentioned in "Making a Murderer." They either did not respond or declined to give interviews.