The sister-in-law of the New York architect accused of a series of Long Island murders said Friday she was «stunned» and «deep» in disbelief following his arrest in the murders of three women more than a decade ago.

Rex Heuermann, 59, was charged last week with three counts of first-degree murder and three counts of second-degree murder in the deaths of Melissa Barthelemy, 24, Megan Waterman, 22, and Amber Lynn Costello, 27. The women’s remains were discovered in December 2010 in Gilgo Beach on Long Island’s south shore.

Dr. Johanna Ellerup, Heuermann’s sister-in-law, said in an email to NBC News on Friday that she is «stunned» and that «this disbelief alone is profound and upsetting.»

The suspect was arrested last week at his home in a quiet suburban neighborhood of Massapequa Park. He has a wife and two adult children.

«I vacillate between desperately wanting my niece and nephew’s life to go back to its previous state, intact, without a father accused of being a serial killer, to being pleased and safe knowing that someone is in custody,» Ellerup said. «My ego has great difficulty processing the idea that I looked Rex in the eye and couldn’t discern any murderous intent.»

He added that his half-sister «is going through an exceptionally difficult time.»

He declined to speak further out of consideration for his family, saying he has no further knowledge of the case.

Heuermann’s wife, Asa Ellerup, filed for divorce on Wednesday, her lawyer said. Attorney Robert Macedonio said a summons and complaint was filed on Asa Ellerup’s behalf in Suffolk County Supreme Court.

Ellerup and his family «are going through a devastating time in their lives,» Macedonio said in a statement to NBC News on Friday afternoon.

«The sensitive nature of her husband’s arrest is taking an emotional toll on the immediate and extended family, especially older family members.»

Authorities have said Ellerup was out of state at the time of the slayings and is not considered a suspect.

The Suffolk County Police Commissioner said this week that Heuermann’s family was shocked when they learned of the allegations against him.

«They were upset. They were embarrassed,» said Suffolk County Police Commissioner Rodney Harrison. told CNN on Monday. «So if you ask me, I don’t think they knew about this double life that Heuermann was living.»

Heuermann is also a suspect in the disappearance and death of a fourth woman, 25-year-old Maureen Brainard-Barnes, whose remains were also found near Gilgo Beach. That investigation is still ongoing, according to a bond request filed on July 14.

All the victims were believed to be sex workers advertising on online sites, according to police.

Rex Heuermann is charged with the murders of Melissa Barthelemy, 24, left, Megan Waterman, 22, second from right, and Amber Lynn Costello, 27, right.  Heuermann is a suspect in the disappearance and death of Maureen Brainard-Barnes, 25, second from left.
From left, Melissa Barthelemy, Maureen Brainard-Barnes, Megan Waterman, and Amber Lynn Costello. Suffolk County Police Department via AP file

The victims, known as the «Gilgo Four,» were discovered during a search for another missing woman, 23-year-old Shannan Gilbert, who was last seen running through the nearby gated community of Oak Beach after leaving a client’s home, according to a report. police timeline.

The police would end up discovering the remains of more than 10 people.

Now, investigators say they are investigating unsolved murder cases across the country for a possible connection to Heuermann, according to Suffolk County authorities, after it was discovered that he has ties to Las Vegas, South Carolina and Atlantic City, New Jersey.