RIVERHEAD, N.Y. — The man accused of killing several sex workers and dumping their bodies on a Long Island beach was charged with two more killings, as prosecutors on Thursday disclosed they’ve unearthed a gruesome “planning document” used to carry out the slayings.

Rex Heuermann, a 60-year-old former architect, was formally told of new charges — second-degree murder in the deaths of Jessica Taylor and Sandra Costilla — in front of Suffolk County Superior Court Judge Timothy Mazzei.

He’s now been charged with killing at least six women.

After Heuermann’s arrest, investigators seized several electronic devices from the suspect, including a laptop with a Microsoft Word document, the indictment said.

That document, titled “HK2002-04” was created in 2000 and was edited numerous times throughout 2002, officials said. It included one section that listed four headings, for “problems,” “supplies,” “DS” and “TRG.”

• The “problems” included possible evidence such as DNA, tire marks, blood stains, foot prints and hair, the indictment said.

• Under “supplies,” the document listed, among other items, rope, tarps, tape, medical gloves and various cleaning agents.

• “DS,” probably stood for “dump site,” investigators said, and listed locations where evidence could be disposed.

• And TRG likely meant “target” and specified that “small is good,” according to investigators who noted that “the known victims thus far are all petite women.”

“The task force believes this is a planning document that was utilized by Heuermann to methodically blueprint and plan out his kills with excruciating detail,” Suffolk County District Attorney Raymond Tierney told reporters outside of court Thursday.

The document found on Heuermann’s computer went on to list other “post event” acts, according to the indictment.

• A “body prep” heading included reminders to “wash body inside and all cavities,” to “remove ID marks” such as tattoos and to “remove head and hands.”

• One listing was for “dispose of the following” and included “tools and devices,” clothes and “anything that touched” the victim.

• And “things to remember” for future acts included reminders such as “get sleep before hunt too tired creats (sic) problems” and to use “heavy rope for neck — light rope broke under stress of being tightened.” The writer also noted that “more sleep & noise control = more play time.”

“His intent, specifically, was to locate these victims, to hunt them down and to bring them under his control and to kill them,” Tierney said. “His motivations, meticulous planning and clear intent is obvious.”

Heuermann was arrested last July 13 as he was casually walking on a busy New York City street after work, apparently unaware he was being followed by police.

He was originally charged with murder in the killings of Melissa Barthelemy, 24, Megan Waterman, 22, and Amber Lynn Costello, 27. Earlier this year, he was charged in the killing of Maureen Brainard-Barnes, 25.

The victims were among several found around Gilgo Beach, on Long Island’s South Shore, in cases that went unsolved for more than a decade.

The 20-year-old Taylor disappeared in July 2003, while working as an escort in New York City, and her remains were found in two grisly incidents, that year and in 2011.

A dog walker in 2003 found Taylor’s body which had been mutilated, with her head removed and arms severed below the elbows, officials said.

A tattoo of hers was also mutilated and “were acts perpetrated by Rex A. Heuermann to … inhibit the identification of the victim via facial recognition, fingerprints and/or tattoo identification,” according to the indictment.

“Ms. Taylor’s skull, hands, and forearm were discovered along Ocean Parkway, just east of Gilgo Beach,” on March 29, 2011, the indictment said.

At the time of Taylor’s slaying, Heuerman’s family was on vacation in Vermont with the family of his daughter’s kindergarten classmate. But Heuerman did not go along, according to the indictment.

A dark-colored Chevy pickup truck, seen parked near where Taylor’s body was found, resembled one that Heuermann owned at the time, the indictment said.

And a hair found on Taylor’s body was matched, with 99.96-percent certainty, to Heuermann, prosecutors said.

Costilla was found by hunters in an wooded area of Southampton on Nov. 20, 1993.

“The victim’s shirt had been pulled up over her torso and head, exposing the victim’s breasts,” according to court documents, describing horrific postmortem wounds. “The victim had numerous sharp force injuries to … her face, torso, breasts, left thigh, and vaginal area.”

Hairs found on Costilla’s body also matched Heuermann with 99.96-percent certainty, prosecutors said.

Heuermann wore a suit and tie with his hands handcuffed behind his back throughout Thursday’s brief hearing.

Heuermann’s attorney, Michael Brown, entered a not-guilty plea on behalf of his client. Outside of court, Brown said he could not immediately discuss the new charges.

“So it’s hard for me to comment without looking at documents and without speaking to my client and looking into the evidence,” Brown told reporters. “It wouldn’t be fair for me to comment at this point in time. I really need to look at everything.”

The judge ordered Heuermann to remain behind bars without bail. His next court date is set for July 30.

DA Tierney said investigators are still looking at several other murders that could be still be linked to Heuermann.

Tierney was specifically asked if the slaying of Valerie Mack, 24, is on the DA’s radar for Heuermann, and he said, “I think that would be fair to say.”

“We’re not going to stop, we can’t stop,” the prosecutor said. “We owe that to the victims. That’s the least we can do.”

Carolina Gonzalez reported from Riverhead, New York; and David K. Li from New York City.

This article was originally published on NBCNews.com