CNN —

Gilgo Beach serial killings suspect Rex Heuermann now faces charges in the deaths of six women spanning three decades and multiple Long Island communities after he was indicted on two new murder charges Thursday — the latest development in an investigation authorities in New York say is far from over.

Heuermann appeared in an eastern Long Island courtroom to face charges of second-degree murder in the 2003 death of Jessica Taylor and the 1993 death of Sandra Costilla, according to a bail application.

“He is not guilty, and he wants you to accept his not guilty plea,” Heuermann’s attorney Michael Brown told the judge. Heuermann was remanded without bail and is expected in court again on July 30.

Taylor’s remains were discovered in Manorville in 2003 and then additional remains along Ocean Parkway on Gilgo Beach in 2011.

A hair found underneath Taylor’s remains was linked to Heuermann, according to the bail application.

Costilla’s remains were found in North Sea in 1993 by two hunters who were in the woods, according to the bail application. She was found with “sharp force injuries” to multiple parts of her body, the document states.

The bail application highlights two different forensic laboratories that were able to determine that the hairs recovered on five of the six charged victims were tied to Heuermann, members of his immediate family or to people he lived with, according to the document.

“Defendant Heuermann is the individual who murdered, stripped, restrained, and transported the remains of Jessica Taylor and Sandra Costilla, as well as the Gilgo Four, until they were each discovered in 1993, 2003, 2010, and 2011,” the bail application reads.

Heuermann was initially arrested in July 2023 and was charged with murder in the killings of four women whose bodies were discovered bound with belts or tape and wrapped in burlap along a stretch of Long Island’s Gilgo Beach in 2010.

Heuermann pleaded not guilty to the charges related to those four victims.

The victims – Melissa Barthelemy, Megan Waterman, Amber Costello and Maureen Brainard-Barnes – became known as the “Gilgo Four.”

The women were among at least 11 sets of remains discovered near the waterfront in Long Island’s Suffolk County since 2010.

Authorities have accused Heuermann of leading a double life, saying they believe his wife and children did not know about the alleged crimes and that the “Gilgo Four” killings allegedly all took place when his family was traveling out of state. That allegedly allowed Heuermann “unfettered time to execute his plans for each victim without any fear that his family would uncover or learn of his involvement in these crimes,” prosecutors previously said in an indictment.

Less than a week after Heuermann’s arrest, his wife filed for divorce. But she has since said she does not believe Heuermann is capable of the crimes he’s accused of.

In January, Brown told reporters the former New York architect claimed he’s “not guilty of these charges” and looks forward to fighting the charges in court.

‘We are not near the end of this investigation,’ law enforcement source says

Law enforcement sources told CNN that investigators uncovered evidence during searches of the Manorville area of Long Island as well as Heuermann’s home earlier this year that helped advance the investigation.

Detectives believe, based on “offender characteristics” of serial killers, there may be more alleged killings, according to officials who have been briefed on the investigation.

“In most of these cases, a serial killer does not start killing in his 40s,” said a law enforcement official familiar with the case.

That belief spurred investigators to not only expand their attempts to identify unidentified victims, re-examine dump sites and conduct additional searches of Heuermann’s home, but to also begin reexamining unsolved missing persons cases.

Investigators are also looking at seemingly unrelated unsolved homicides where there may be similarities among the victims, the crime scenes or condition of the bodies.

“We are not near the end of this investigation,” one law enforcement official involved in the sweeping case said. “We are very much at the beginning.”

CNN’s John Miller, Emma Tucker and Ray Sanchez contributed to this report.