Nathan Mendes is still haunted by the 2008 murder of salesman Travis Alexander and the media spectacle that ensued.

Alexander was a 30-year-old Mormon whose body was discovered in his shower by friends. He was stabbed nearly 30 times and shot in the head with a .25 caliber pistol.

His ex-girlfriend Jodi Arias, who insisted at the time two masked intruders attacked her and killed Alexander, was found guilty in 2013 of first-degree murder. Prosecutors said it was a premeditated act carried out in a rage after Alexander wanted to end their romance and later planned a trip to Mexico with another woman.

Her trial stirred headlines for televising salacious evidence, along with shocking testimony depicting the couple’s stormy relationship. The slaying also inspired numerous books and TV specials and would also become the subject of a 2013 Lifetime film titled “Jodi Arias: Dirty Little Secret.”

And now for the first time, the former detective for Siskiyou County, California, who arrested Arias at her grandparents’ home after it appeared she was on the move, is coming forward.

He discusses his involvement in the explosive investigation and trial in the three-part limited series on Investigation Discovery (ID) titled “Jodi Arias: An American Murder Mystery.” The special explores the death of Alexander and the subsequent legal circus as Arias was tried.

Mendes told Fox News he’s hoping it will help audiences focus on Alexander instead of Arias.

“I think people should realize the whole thing is a travesty,” he said. “As sad as it is, everybody focused on Jodi. Books are named Jodi Arias, shows have the name Jodi Arias. Taglines are Jodi Arias. It’s almost like we forgot Travis even existed in all of this. It became such a circus about Jodi.

"And she shouldn’t be the headliner here. And hopefully, some people will get to see that other side and realize Travis was the victim here. Jodi made that decision, but we shouldn’t have ever highlighted her. Books and shows should be based on Travis Alexander, not Jodi Arias… I think Travis and his family deserve that.”

Travis Alexander (Courtesy of ID)

Still, Mendes admitted there was no denying Arias’ strange behavior after her former lover was savagely killed in his own Mesa, Arizona, home.

“The crime scene was such a mess,” he said. “… But when I first came across Jodi and we arrested her at her grandparents’ house, my initial impression of her was she didn’t seem concerned at all… The whole case was bizarre. Especially her demeanor… Even when we booked her, she wanted to make sure her hair looked OK… Things like that were not sitting well with a lot of us.

"She was almost more concerned about her image… She didn’t have a concern for consequence or outcome… Like for me, I wouldn’t care what my hair looked like if I was being arrested or what my picture is going to look like. To me, that was just weird.”

In the show, Mendes shared how he observed Arias while she was being interrogated and the jaw-dropping behavior that quickly followed.

Detective Nathan Mendes (right) during the trial of Jodi Arias. (Courtesy of ID)

Arias, who was initially sobbing through a four-hour police interrogation, dramatically changed her attitude when the prosecutor left the room. She was seen talking to herself, laughing, singing, playing with a garbage can and doing a headstand against the wall.

“At the time, we were watching it from the next room,” recalled Mendes. “She was trying to burn off stress. That was an indicator of stress. When people are put under a lot of stress that energy has to go somewhere, so you do see a lot of bizarre things in the interrogation room. She was just kind of rambling. But the whole yoga scene was a little strange to me. I’ve seen some strange things, but that’s up on the top.”

During the trial, Arias attempted to depict herself as a physically and emotionally battered woman who was forced to satisfy the perverted demands of her lover. However, it was revealed in court Arias was willing to chronicle her sexual escapades with Alexander through photographs and recordings.

“I was a little surprised by the relationship that they had,” said Mendes. “And the relationship she had with other men. Sexually. I know everybody has their private lives that they don’t share with other people. But that was the thing with Jodi. The world got to see it.

Jodi Arias during her trial. (Courtesy of ID)

"For a lot of folks that was the first time they had seen someone’s sexual exploitations plastered all over the media. And that was shocking for a lot of people. You read about it and you certainly hear about it, but in her case, it was just put out there.”

Mendes also revealed Arias’ family, whom he described as “hardworking” and “normal,” were stunned by their daughter’s horrific actions.

“She has a great family,” he said. “They were devastated. Absolutely devastated… I know initially they were dumbfounded and it was kind of surreal to them as far as her grandparents and parents were concerned. It was like, ‘You guys must have made a mistake.’ That was their initial reaction. ‘You have the wrong person.’ And that’s normal behavior from parents, family members. No one wants to think that their child, [or] grandchild, can do something that brutal to anybody.”

Still, Mendes claimed Arias had no intention of becoming a celebrity.

Jodi Arias' strange behavior and determination to look great in her mugshot stunned law enforcement. (Siskiyou County Sheriffs Office / Courtesy of ID)

“I think unfortunately, she was sensationalized by the media and I think at some point, it just got addicting. And she kind of ran with it. I don’t know if she had any intentions of making it about her. [But] a spotlight was put on her and she became sensationalized. I think that’s just the way things went.

"And that’s what happens when the media a lot of times get involved. Everybody was just so shocked by what happened and then the trial became a circus. I don’t think anybody had any intentions of it. It just happened, going the way it did.”

In 2015, Arias was sentenced to life in prison without parole. Mendes is now a supervisory special agent for the Department of Justice.

Mendes said Arias was motivated to kill.

Audiences were shocked to hear about the stormy, sexual relationship Jodi Arias and her ex-boyfriend Travis Alexander shared before his 2008 murder. (Reuters)

“I think she just wasn’t willing to share him with anybody else,” he said. “That’s my personal opinion. Just seeing the evidence and seeing what was transpired before Travis was killed.

"I think she had come to the realization that Travis wasn’t going to settle down with her and that she wasn’t willing to share him with anyone else or have him date or marry anybody else. It had to be Jodi. I think that’s what prompted a lot of this. She wasn’t willing to let him go. It’s the old, ‘If I can’t have you, nobody can.’”

Part two of “Jodi Arias: An American Murder Mystery” airs Monday, January 15th at 8 p.m. on ID.