You don’t have to be crazy to feature in David Fincher hit psycho-thriller Mindhunter but clearly it helps. Season two of Fincher’s chronicling of the groundbreaking FBI behavioural science unit, and its investigations into serial killers through the ’70s and ’80s, brings us the “Son of Sam”, the Atlanta child murderer and – ironic drum-roll – Charles Manson himself.

It’s extraordinary television. Even more so because it finds a way to convey the grisliness and sheer evil of these sociopaths without glamorising their deeds or trampling over the memory of their all-too real victims. Alongside that it plunges into the personal lives of BSU special agents Holden Ford (Jonathan Groff), Bill Tench (Holt McCallany – educated in Newbridge College, Co. Kildare of all places) and psychological consultant Wendy Carr (Anna Torv).

Fincher has form when it comes to the genre of course. He gave us the two definitive serial killer movies in Seven and Zodiac. The former was heightened horror (“what’s in the box!”), the latter an exquisite slow-burn that refused to send its audience away with a neat resolution. Mindhunter, in its second season especially, is different. It is neither as grandly baroque as Seven nor as nihilistic as Zodiac.

This Fincher has explained was part of his broader vision. With his Netflix series he wanted to remove the mystique that has accumulated around the serial killer (something he himself contributed to, it should be acknowledged). The point he wished to convey is that few if any real life killers are in the Hannibal Lecter mould. “I don’t want to talk about the gourmet opera expert,” he said. “To me these are very sad people, who have grown up under horrendous circumstances. This is not to overstate how much empathy or sympathy we should have for them, but it’s just simply a fact… We’d seen so much of this literary conceit of: there’s a very fine line separating the hunters from the hunted. And I really thought it was time to take that back and make it, really, the reason that we are fascinated with them is because we’re nothing like them. They are unfathomable.”

“From the very first meeting we had about the show, David Fincher’s mission statement has always been that he doesn’t want to make comic book villains of serial killers,” Groff added to Vanity Fair. “He wanted to show them as the sad, deplorable human beings that they are, and to explore their psychology. In no way did he ever want to celebrate the serial killer, and every single day on set operated with that mission and goal at the forefront. There is that temptation, in our cultural obsession, to make the killers powerful again by investing in them. We’re interested in taking an honest look and doing the opposite.”

Mindhunter is, in its way, just as ambiguous at Zodiac. That film was based on the true life case of the Zodiac killer who stalked San Fransisco in the ’70s and was never caught. Mindhunter is adapted from the memoirs of FBI behavioural science unit special agent John Douglas – the Ford character on screen – and so likewise drawn from the FBI files. That means the featured cases don’t always have tidy conclusions. The Atlanta Child Murder storyline in the second series, for instance, ends on what might be deemed an unsatisfactory note. It certainly isn’t an open and shut story in which the good guys ride to the rescue. Atlanta’s racial and social schisms are there humming in the background, complicating the investigation. For Fincher, TV is the perfect medium with which to weave these knottier narratives.

“I learned my lesson with Zodiac,” he said. “You can ask a lot of an audience, but 2 hours 45 minutes and no closure...it’s asking a lot.” “Asking a lot” is something the cast of Mindhunter will be intimately familiar with. Fincher, who directed the opening three hours of season two, is one of the most celebrated and notorious filmmakers working today. He’ll do take after take and is known to be bizarrely specific about certain aspects of the job (a pet peeve is characters moving their foreheads in a shot).

Add to that the grisly subject matter and it’s no surprise that it can all get under the skin of the actors. “I compartmentalise the work on the show,” said Groff. “Serial killers aren’t my jam in that way.”

Creepy and claustrophobic it may be, but Mindhunter is also one of the most addictive shows on TV and many fans will have binged all nine episodes in just a few sittings. The good news is that Netflix has a thrilling second course in the works. Globe-hopping new crime series Criminal will take viewers inside police interrogation rooms in Spain, France, Germany and the UK. The whole thing is filmed at Netflix’s Madrid production facilities, with three of the 12 episodes devoted to each country. The goal is to convey the nitty-gritty of police work as a suspect is grilled (though hopefully not battered) for the truth. The cast is top-notch, with the UK portion featuring David Tennant, Hayley Atwell, Rochenda Sandall from Line Of Duty, Nicholas Pinnock from Marcella and Shubham Saraf from Bodyguard. It’s out September 20 and we can’t wait.

• Mindhunter season two is on Netflix now. Criminal debuts September 20.