The man charged with killing seven women and scattering their remains throughout Long Island, New York, pleaded guilty on Wednesday, marking the end of a decades-long case that instilled fears of a serial killer lurking within the region. 

Rex Heuermann, a 62-year-old architect, admitted to murdering Melissa Barthelemy, Megan Waterman, Amber Costello, Maureen Brainard-Barnes, Jessica Taylor, Sandra Costilla, and Valerie Mack. 

He also took responsibility for the uncharged murder of Karen Vergata.  

In court on Wednesday, Heuermann said each woman’s cause of death was by strangulation. He will be sentenced on June 17. 

Before Heuermann changed his plea, Suffolk County District Attorney Ray Tierney asked him to confirm details surrounding each murder as members of the victims' families were heard gasping and audibly crying in the courtroom gallery. 

"On or about July 6, 2010, did you meet Megan Waterman with the intent to cause her death and did you cause her death?" Tierney said. 

"Yes," Heuermann replied. 

Tierney went on to ask how Waterman – along with the other victims – were killed. 

"Strangulation," Heuermann confirmed as Tierney asked about each victim's death, one-by-one. 

WATCH: Gilgo Beach serial killer Rex Heuermann pleads guilty

Heuermann's ex-wife, Asa Ellerup, and daughter, Victoria Heuermann, could be seen holding hands and clutching tissues as they listened. 

"My thoughts and prayers are with the victims and their families," Ellerup told reporters outside the courthouse immediately following the plea. "Their loss is immeasurable. And the focus should be on them at this time and moment. I ask that you give some privacy to my family as they navigate through this very difficult time." 

Heuermann has also agreed to work with the FBI's Behavioral Analysis Unit to be studied by federal officials as part of his agreement with prosecutors, according to his attorney. Brown said Heuermann has an obligation to be "truthful, accurate and complete" with the FBI.

"A defendant also has an absolute right to change his plea to accept responsibility and enter a plea of guilty," defense attorney Michael Brown said Wednesday after the guilty plea.

"That decision is ultimately up to the defendant," Brown added. "He controls his case, and that's his prerogative. That's his right. And that's what happened here today, when Rex decided that he wanted to accept responsibility and didn't want to proceed to trial." 

Heuermann was arrested outside his midtown Manhattan office in July 2023 and had maintained his innocence for nearly three years. A trial had been set for September.

The Gilgo Beach investigation was thrown into the spotlight in 2010 after police discovered numerous sets of human remains along an isolated beach highway on Long Island, while searching for 23-year-old Shannan Gilbert, evidence gathered from newly-released DNA technology would be admissible at trial, with prosecutors claiming the evidence directly connected Heuermann to the murders. 

Heuermann is expected to be handed three consecutive sentences of life in prison without the possibility of parole for the murders of Barthelemy, Waterman and Costello, along with an additional consecutive sentence of 100 years to life for killing Brainard-Barnes, Taylor, Costilla and Mack, the Suffolk County District Attorney's Office said in a statement. 

In exchange for his admission to the killing of Vergata, the additional plea has been added to Heuermann's plea to the seven murders. 

Fox News' Jennifer Johnson, Tessa Hoyos and Michael Ruiz contributed to this report.