Thirty years ago today, one of America's most notorious serial killers, Ted Bundy, was executed at the Florida State Prison. Bundy had spent the previous decade on death row maintaining his innocence; only when his execution became inevitable did he finally confess to the brutal murder of upwards of 30 women in seven states between 1974 and 1978.

On Thursday, coinciding with the anniversary of Bundy's death, comes a four-part Netflix series, Conversations With a Killer: The Ted Bundy Tapes, which draws from more than 100 hours of previously unheard interviews with Bundy while he was awaiting execution. Yet even as director Joe Berlinger invites audiences into the mind of pure human evil, he builds an uneasy case against Bundy's 1989 execution. While never truly explicit — Berlinger also gives Bundy's fiercest critics a chance to justify the nature of his punishment — the documentary doesn't leave you with relief that Bundy was finally destroyed so much as it does an overriding queasiness with the violence in human nature.

Conversations With a Killer follows Bundy from his first verified killings, in Seattle's University District in 1974, through his multiple escapes from custody, and eventually to his capture and death in Florida. The documentary is unflinching in its depiction of Bundy's crimes — Berlinger includes graphic photographs of crime scenes and uncovered human remains — even as Bundy smugly maintains his innocence on the tapes. Only when asked, through a bit of clever flattery, to use his psychology degree to profile the kind of man who would murder young women does Bundy flirt with a confession — a sort of early version of O.J. Simpson's If I Did It.

To be clear, there is no doubt that Bundy is a monster; rather, the documentary's final section raises questions about the American criminal justice system and the use of capital punishment within it.

First, there is the initial murder case itself, which lacked proof beyond a trace of a doubt that Bundy was the perpetrator in the bludgeoning of Chi Omega sorority girls at Florida State University. The case hinged on a potentially unreliable witness as well as work by an odontologist who claimed Bundy's crooked canines matched bite marks on one of the victims, a form of dental forensics that is now considered to be "junk science." This isn't to suggest that Bundy was innocent — he certainly wasn't, as a later, much more convincing trial would determine — but that all it takes is "prejudicial publicity" to persuade a jury to deliver a guilty verdict, even if firm evidence isn't there.

Additionally there is the fact that Bundy was not only ruled competent to stand trial, but that he served as his own co-council. Bundy repeatedly "sabotaged" himself in this role, frustrating his defense team that had begged him to take a plea bargain for a 75-year sentence. "The most important thing was to save his life," emphasized Michael Minerva, the public defender assigned to Bundy's case. But Bundy declined, and his erratic behavior in court continued. It "really just confirmed to me that he did not have a rational understanding of the proceedings," said defense lawyer Margaret Good. Likewise, a Yale psychologist asked to assess Bundy "was extremely confident that there was something unique about Ted's brain that had led to this," said Polly Nelson, who was Bundy's post-conviction counsel. She goes as far as to question whether he could control himself at all.

Berlinger balances the questions he raises about capital punishment in Bundy's case with the voices of death penalty advocates. "I feel that there are some people who, by the enormity of their crime, forfeit the right to live," said George Dekle, who served as a prosecutor against Bundy and would later be a witness to his execution. Or, as former Florida Gov. Bob Martinez (R) is seen in archival footage telling the news, "[Bundy] represents why you have capital punishment."

At the same time, Berlinger does not flinch from the ugly details of Bundy's execution, either. The documentary includes footage of the celebration that sprouted outside the prison ahead of Bundy's electrocution, described by one witness as being a "carnival." "There were thousands of people outside, you could hear them even in the inner confines of the prison," recalled FBI Special Agent Bill Hagmaier. "'Burn, Bundy, burn. Burn, Bundy, burn' ... I looked at Ted and said, 'You hear that out there?' And he said, 'They're crazy. They think I'm crazy. Listen to all of them.'" And listen we do — to archival videos of celebrants' whooping, singing "hey, hey, hey, goodbye," and to vendors selling T-shirts and electric chair buttons. Other attendees held signs that read "Hey Ted, this BUZZ is for you," "Teddy, you're the toast with the most," and, simply, "Have a seat, Ted." Conversations convincingly portrays the scene as being as raucous and sickening as a medieval public hanging.

Just as Berlinger had shown Bundy's monstrousness over the previous three hours, he finds its palest reflection in the justice that is carried out in retribution. Bundy's mother makes the spiritual case against her son's death: "My Christian upbringing tells me that to take another's life under any circumstances is wrong," she told the news, "and I don't believe the state of Florida is above the laws of God." Even Dekle, the prosecutor who took Bundy to court "to make sure — certain — that he was executed," expressed horror at his own emotion over seeing a man put to death. "I'm ashamed to admit that I was elated," Dekle confessed. "I hope I'm never happy over the death of another human being ever again."

Berlinger has made his career out of interrogating what he calls the "sanity of the death penalty," having focused on wrongful convictions and racial bias in other cases as being "a wake-up call for how broken capital punishment is in this country." Conversations With a Killer, though, is far from a passionate crusade against capital punishment; featuring hours of Bundy's unimaginable crimes, the movie makes death seem like the only fitting option. But, if there's a lingering sense of unease with the electrocution of one of America's worst serial killers, then how can we be certain similar punishments are conscionable?

Conversations With a Killer never offers a simple answer. All it gives us, in the end, are Bundy's own words: "Vengeance is what the death penalty really is," he says on the tapes. "Really, it's a desire of society to take an eye for an eye. And I guess there's no cure for that."