The stomach-churning notes accused Gilgo killer Rex Heuermann kept about grisly murders — including morbid ‘lessons learned’

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Accused Gilgo Beach serial killer Rex Heuermann kept a stomach-churning “planning document” mapping out his grisly slayings — which even included a chilling “Things to Remember” section and a morbid “Lessons Learned” section, officials revealed.

A computer “allocated space” file that Heuermann allegedly tried to delete laid out a gruesome road map of the vicious murders of six sex workers dating to 1993 — including the decapitation and mutilation of two victims newly tied to the hulking Long Island dad, Suffolk County prosecutors said Thursday.

In one disturbing notation, Heuermann allegedly indicated he planned to keep killing, prosecutors said.

“The GIlgo Homicide Task Force members believe these references to ‘next time’ indicate Heuermann’s prior experience and what changes to implement moving forward,” the DA’s filing said.

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The revelation came as the DA’s office slapped Heuermann with new charges in the 1993 slaying and mutilation of Sandra Costilla and decapitation and dismemberment of Jessica Taylor in 2003 — on top of the pending felony charges he already faced in the deaths of the women known as the “Gilgo Four.”

According to a bail application filed by prosecutors Thursday, Heuermann maintained a secret digital record titled “HK2002-2004” on his computer since at least 2000, keeping precise notes on the murders.

The digital document was broken up into specific sections like “Problems,” “Supplies,” “TGR,” which prosecutors said are believed to be potential targets, and “DS,” allegedly for “dump sites.”

The sick how-to file notes that “small is good” for potential victims, and includes a three-part section for “Pre-Prep,” “Prep” and “Post-Event,” the Suffolk DA’s court document said.

“The HK planning document continues to further expound on preparatory measures such as specific ‘recon’ steps taken,” including “packaging [a body] for transport,” prosecutors said.

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One section notes to “remove head and hands,” which the DA’s office said is consistent with the remains of Taylor and another Gilgo body, Valerie Mack, which has not been officially tied to Heuermann.

Also included is a section reminding the accused killer to “remove ID marks [tatoos] [sic],” which is consistent with Taylor’s remains, which had “linear injuries,” particularly “around where Ms. Taylor’s tattoo had been located, which investigators believe was intended to inhibit the identification” of the victim.

Finally, Heuermann allegedly kept a “Things to Remember” section, which detailed twisted reminders such as to “hit harder” for “next time” and to use heavier rope because the “light rope broke under [stress of being tightened].”

“Hit harder too many hit to take down,” the planning document says, according to prosecutors.

“Consider a hit to the face or neck next time for take down.”

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In addition, Heuermann opines on the importance of sleep to avoid “problems” and increase what he refers to as “play time,” prosecutors said.

Also in that section are notations for “push pins to hang drop clothes from ceiling” and “not tape,” and notes on “sound travel” — indicating a preference for committing crimes indoors, the DA said.

According to prosecutors, the HK file “points to Heuermann’s self-education and ‘homework.'”

Heuermann, a 60-year-old architect from Massapequa Park with offices in Midtown Manhattan, is charged with killing a half-dozen sex workers over the past three decades.

The murders of the victims — Taylor, 20, Megan Waterman, 22, Melissa Barthelemy, 24, Maureen Brainard-Barnes, 25, Amber Lynn Costello, 27, and Costilla, 28 — remained unsolved for decades until the slayings were reopened in 2022 and led to Heuermann’s arrest in July.

Costilla, who disappeared in 1993, had not previously been tied to the other bodies found along Ocean Parkway, where six other bodies were found, cases that remain unsolved.

Costilla was initially believed to be tied to convicted serial killer John Bittrolff, but the documents filed Thursday by prosecutors said her DNA did not match him.

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