Rex Heuermann left his office near the Empire State Building and strolled down a still-bustling Fifth Avenue as the sun set on a hot Thursday evening in Manhattan.

The 59-year-old architect, whose customers included Catholic Charities, American Airlines and other tenants at John F. Kennedy International Airport, is seen in video obtained by CNN affiliate WABC walking calmly at the end of a work day. A bag was slung over his shoulder, his left hand in his pocket, when he's approached by several men in dark suits and ties.

Tall and heavyset, Heuermann towered over the law enforcement officers who now surrounded him. As passersby strolled leisurely along the avenue, he was taken into custody without incident in connection with a 13-year homicide investigation involving young female victims on the South Shore of Long Island.

"Yes, the day has finally come when someone so ... depraved of heart who would kill individuals, innocent individuals in the prime of their lives, their young lives, is finally brought to justice," New York Gov. Kathy Hochul said Friday. "We are hoping that this will bring justice to this individual but also peace to the families."

That day came -- finally -- years after a bestselling nonfiction book, a Netflix drama, and a podcast about a long-running murder mystery that made national headlines and become known as the Gilgo Beach killings.

Heuermann is charged with three counts of first-degree murder for the killings of Melissa Barthelemy in 2009, and Megan Waterman and Amber Costello the following year, according to the Suffolk County District Attorney.

The alleged killer had been living a double life in a Long Island village a short drive from where their remains were found, prosecutors said.

Heuermann, who told his attorney he's not the killer, is also the prime suspect in the 2007 disappearance and death of a fourth woman, Maureen Brainard-Barnes, according to a bail application from Suffolk County prosecutors. He has yet to be charged in the case.

The victims, who worked as escorts, became known as the "Gilgo Four."

On Friday, Heuermann was ordered held without bail after pleading not guilty during a first court appearance.

Heuermann was in tears following his arrest.

"I did not do this," his court appointed attorney, Michael Brown, said his client told him.

A crucial break in the case came in January when investigators took a swab from leftover pizza crust Heuermann discarded in the trash outside his Manhattan office, according to the bail application.

DNA evidence linked him to a hair found on the burlap sack where Waterman's remains were found.

Living a double life

The son of an aerospace engineer, Heuermann lived with his spouse and children in the homey village of Massapequa Park, across the bay from where the remains were found, on the southeastern edge of Nassau County.

In a video interview posted online last year, as police in Suffolk County formed a multiagency task force to investigate the long-dormant cases, Heuermann said he was born and raised on Long Island. He had been working as an architectural consultant in Manhattan since 1987.

"I do troubleshooting, architectural troubleshooting, and negotiations with the building department," Heuermann said.

"When a job that should have been routine suddenly becomes not routine, I get the phone call," he added.

His father had built satellites for a living, Heuermann told the interviewer. His dad also built furniture in a workshop in the house Heuermann grew up in and still lived with his family.

Asked what his job taught him about himself, Heuermann said: "I think it's taught me more about how to understand people. Dealing with the technical aspects is something a person can learn ... But it's the people, how they're all so different and how you deal with the people, I think, is one of the more interesting aspects that has come out of this."

RH Consultants & Associates was founded by Heuermann and incorporated in 1994, according to the company website.

At the end of his online video, Heuermann put on a pair of sunglasses and posed for a selfie with his interviewer.

"Can you smile?" Heuermann was asked.

"That is," he replied, indicating he was smiling.

Piecing together a complex puzzle

It took investigators nearly 15 years to track down Heuermann.

They first connected him to the killings last year while conducting a review of evidence under a newly formed task force, which included the Suffolk County Police Department, the Suffolk County Sheriff's Office, the New York State Police and the FBI.

In March 2022, investigators found that a first-generation Chevrolet Avalanche -- the same type of truck a witness believed to have been driven by Costello's killer -- registered to Heuermann at the time of the murders, according to the bail application.

Armed with more than 300 subpoenas and search warrants, investigators began to close in on Heuermann.

Evidence revealed the killer had used burner phones to contact victims. Investigators found calls to the victims originated from locations connected to Heuermann.

Investigators said they narrowed cell tower records from thousands of possible individuals down to hundreds and then to a handful of people. They focused on residents who matched a physical description provided by a witness who had seen the killer.

Task force members also learned Heuermann lived close to one Long Island cell site and worked near New York City cell sites where other calls originated.

A series of "taunting" calls in which a male caller admitted killing and sexually assaulting Barthelemy were made from her phone to her family members from the vicinity of Heuermann's midtown Manhattan office during the summer of 2009, according to the bail application.

Heuermann also used burner phones to contact sex workers or massage parlors, the bail application said. And he created false names for an email account used to search for "sex workers, sadistic, torture-related pornography and child pornography," the bail application said.

One fictitious email account was used to send selfies "to solicit and arrange for sexual activity." Another was used to search for podcasts and documentaries about the investigation, as well as "images depicting the murdered victims and members of their immediate families," according to the bail application.

Between March 2022 and June 23, Heuermann used the same account to conduct more than 200 searches about serial killers and articles about the task force investigating the Gilgo Beach killings, the bail application said.

A rag a bone and a hank of hair

A key break in the case came when investigators recovered Heuermann's DNA from pizza crust in a crumpled box he discarded in a Manhattan trash can in January.

The initial examination of Waterman's skeletal remains turned up a male hair from the "bottom of the burlap" the killer used to wrap her body, according to prosecutors. Analysis of DNA found on the victim and the pizza showed the samples matched.

Additionally, hair believed to be from Heuermann's wife was found on or near three of the murder victims, according to the bail application. The DNA was collected from bottles inside a garbage can outside the Heuermann home.

The hairs were found in 2010 and had degraded. DNA testing at the time yielded no results but recent mitochondrial DNA testing allowed investigators to make the connection, according to Tierney.

Heuermann's wife and children were out of the state when the three women are believed to have been killed, Tierney said. Investigators said his wife's hair may have been transferred to the victims from his clothing.

Authorities, fearing the Heuermann might be tipped off they were closing in, moved to arrest him Thursday night.

"We were playing before a party of one," Tierney told reporters. "We knew the person responsible for these murders would be looking at us."

Seeking closure

The case started with the search for a missing woman in 2010, leading to the discovery of multiple sets of human remains at Gilgo Beach.

By the time the remains of the missing woman, Shannan Gilbert, were found one year later, at least 10 sets of human remains had been recovered across two Long Island counties.

Tierney said Saturday the work of the task force is not over.

"There are a lot of other victims, you know, in that area," he told CNN. "There are a lot of victim's families that want closure. So that's what you work towards."

Authorities believe the death of Gilbert, whose disappearance sparked discovery of the other victims, may have been accidental and not related to the other killings.

The remains of the Gilgo Four were found in bushes along a quarter-mile stretch of Ocean Parkway in Oak Beach over a two-day period in 2010.

The skeletal remains of Barthelemy were discovered near Gilgo Beach on December 11. Barthelemy, who was a sex worker, was last seen July 12, 2009, at her apartment when she told a friend she was going to see a man, according to a Suffolk County website about the killings.

The remains of three other women were found on December 13, 2010: Brainard-Barnes, who advertised escort services on Craigslist and was last seen in early June 2007 in New York City; Amber Lynn Costello, who also advertised escort services and was last seen leaving her North Babylon home in early September 2010; and Waterman, who also advertised as an escort and was last seen in early June 2010 at a Holiday Inn Express in Hauppauge.

Heuermann was surprised when he was surrounded by officers and taken into custody near his office on Thursday night, according to Tierney.

Speaking of the arrest, Suffolk County Police Commissioner Rodney Harrison said Friday: "Rex Heuermann is a demon that walks among us. A predator that ruined families. If not for the members of this task force, he would still be on the streets today."