"48 Hours" goes on a global manhunt to find the shadowy figure behind murder-for-hire sites in "Find Yura — Manhunt on the Dark Web."

Alexis Stern, 19, says when police in her home town of Big Lake, Minnesota, told her last year that someone with the alias Mastermind365 wanted her dead, she thought the cops were joking. But when she learned Mastermind365 had sent her picture and personal details to a shadowy figure known as Yura, who ran a dark web murder for hire site — and paid for the hit — she says she knew it was no joke.

In 2016, she was a 15-year-old high school sophomore. Like many people her age, Alexis had been struggling with her self-esteem, when a friend introduced her to a 20-year-old man online.

"I ended up meeting a guy named Adrian," Alexis told "48 Hours" correspondent Peter Van Sant.

Adrian was a video gamer and, much to Alexis's delight, he was English.

"I was always partial to British accents, so I thought it was kind of a bonus," she said. "I wanted to have a boyfriend and it was a perfect opportunity."

Alexis Stern, left and Adrian Fry Alexis Stern

Before long, Adrian was visiting Alexis in Minnesota. She was flattered by the attention, but she says she came to realize things were moving much too fast. She says she came to find him controlling and in 2018 she broke it off. Alexis says Adrian reacted angrily, basically telling her she deserved everything bad that happened to her. She felt Adrian was sending her a message.

"And what is that message?" asked Van Sant. "That … it's not going to end great for me," Alexis replied.

She says she was even more unnerved when she began comparing her emails with Adrian to Mastermind365's dark web hit order. Originally issued as a kidnap contract, she realized Mastermind365 had upgraded his order to murder. What struck her was the date. The kill order had been issued the day after she'd told Adrian Fry she was in a new relationship with someone else.

And it wasn't just the timing of the hit order that seemed suspicious. She says the language in it was hauntingly familiar too. Alexis realized both Adrian and Mastermind365 used phrases common in British English — complete with some of the same typos. Both sometimes referred to themselves with a lowercase "i." And, in a quirk that would become more significant later, both had written "thankyou" as one word.

By the time "48 Hours" learned about Mastermind365, we'd already been investigating Yura and his dark web hit man sites for years. In 2016, a 36-year-old Minnesota dog trainer named Amy Allwine had been murdered by her husband Stephen. We discovered Stephen Allwine had hired Yura to arrange Amy's murder. But he'd grown impatient when Yura didn't deliver, so he had shot his wife himself.

While investigating the Allwine case, we met an English hacker named Chris Monteiro, who had been monitoring Yura's dark web operation for nearly five years. Monteiro had found a way to harvest Yura's sites for information about the murder targets. He later passed the information to "48 Hours" and we notified authorities. In all, we helped expose about 20 active murder plots, leading to four arrests, convictions and prison sentences.

Our work with Monteiro also helped confirm what we had come to suspect : Yura's hit man-for-hire sites are scams. But that's little comfort to the targets like Alexis Stern because, as Stephen Allwine proved when he took matters into his own hands, the high-paying customers are all too real. As if to underline the point, Alexis remembered one of Mastermind365's last messages to Yura, that still sends shivers up her spine.

"I am looking for a pistol with a suppressor," Mastermind365 wrote.

In 2018, we tried to meet Yura for an interview. He stood us up, but later sent us videos, explaining his operation: "You can submit your orders to kill the people you hate," he told us.

Yura -- the alleged mastermind of dark web murder-for-hire sites -- as seen in a video diary shared with "48 Hours." Yura

A few months later, we aired our first story, "Click for a Killer." After it aired, Yura wrote us that our report had dampened his business. And he surprised us by saying he was going legit.

"I opened a restaurant business … and I live nice," Yura wrote.

We again asked to meet with him, but he refused. So last summer, "48 Hours" hired a dark web intelligence analyst, who we're calling Lisa, to help us launch a global manhunt to identify and locate him.

"Looking for criminals on the dark web … is not for the faint of heart," Lisa told us.

We began following a trail of digital breadcrumbs that would lead to England, India, and the Eastern European country of Moldova, before culminating in a stunning confrontation last January in the last place we ever expected — Queens, New York.

Lisa had discovered evidence suggesting someone in Queens had used the same unusual password as Yura had used on the dark web. We learned someone in the same family had apparently once used an email address including the words "gun" and "killa." He had registered a tech company which seemed to have almost no online footprint and, like Yura, had recently opened a restaurant. In early January, we confronted the man on a public sidewalk.

"Our investigation of murder for hire on the dark web has led us here….and I want to ask you…are you Yura?" asked Van Sant. "Who?" the man replied. "Yura," said Van Sant.

"I don't know what you're talking about," said the man.

Later the man repeatedly denied being Yura. He offered to meet with us off camera, but then became angry.

"Stop recording right now. I'm gonna smack the s--t out of your camera."

After watching video of the encounter, in which he eventually struck our camera, injuring our cameraman, Lisa said she became still more convinced he was hiding something — even though he later apologized.

"Based on my experience, innocent people don't hit other people," she said.

"48 Hours" wanted to ask Adrian Fry about the hit order on Alexis Stern. So, we tracked him to a house in the city of Bath, England. His brother said he wasn't home, so we texted Adrian to ask for an interview. He replied:

"I can assure you that I did not go to the online web to hire a hit man or anyone to kill Alexis …"

He texted us again to decline an interview:

"Thankyou for the opportunity," he wrote.

But in his message, we noticed something that startled us. Just like Mastermind365, Adrian again had written "thankyou" as one word.