For months, as 18-year-old Payton Gendron formulated a plan to kill dozens of Black people in Buffalo, he worked to keep his racist plot a secret from his family, according to Gendron’s postings online.

“I literally can’t wait any longer, my parents know something is wrong,” he wrote on April 15, musing about when to carry out a planned shooting that took place Saturday, leaving 10 people dead at a Buffalo supermarket.

The writings were uploaded to Internet file-sharing sites in two batches in recent weeks after apparently being posted on the messaging platform Discord from November through early May. They reveal a teenager intent on keeping his parents in the dark not only about preparations for mass murder but also about the quotidian details of his life. They help fill out a portrait of a young man who described himself as isolated from family and as someone who had few friends and found refuge in hate.

Gendron wrote that his parents were unaware of the powerful weapons he was acquiring and hiding in his bedroom, and did not know he was buying and selling silver coins to finance his ammunition purchases. He wrote that he repeatedly lied to them about attending a local community college he had secretly quit this year. He fretted about the possibility that they would discover his subterfuge.

“My parents know little about me,” he wrote on Feb. 22. “They don’t know about the hundreds of silver ounces I’ve had, or the hundreds of dollars I’ve spent on ammo. They don’t know that I spent close to $1000 on random military s---. They don’t even know I own a shotgun or an AR-15, or illegal magazines.”

Gendron, from Conklin, N.Y., has pleaded not guilty to first-degree murder. His lawyer did not respond to a request for comment.

Gendron’s parents, both civil engineers for the state of New York, did not respond to messages seeking comment. Efforts to reach them through friends and relatives were also unsuccessful.

Gendron’s father, Paul, has long been active in one of New York’s largest labor unions for state employees, the Public Employees Federation. He sits on the union’s executive board and chairs a statewide committee focused on labor-management issues at the state’s transportation agency, PEF President Wayne Spence said in a statement.

In an appearance before the New York State Assembly in 2017 to testify about the transportation budget, Paul Gendron said he had worked at the agency for 23 years. Payton Gendron’s mother, Pamela Gendron, also works at the state transportation agency as a traffic operations engineer, according to agency documents.

Payton Gendron espoused the “great replacement theory,” an idea popular among the far right that holds that there is a conspiracy to replace native-born Americans with immigrants. There is no evidence in his parents’ limited online footprint that they shared those views.

Their Twitter accounts show that they follow mainstream media sources. A registered Democrat, 51-year-old Paul Gendron has retweeted messages from President Biden and Transportation Secretary Pete Buttigieg. Pamela Gendron, 53, a registered Republican, follows celebrities and entertainers and no apparent political figures.

The Gendrons have owned their home in Conklin — a small, majority-White suburb of Binghamton on New York’s southern border — since 2002. The three-story light-blue structure has a big, neatly mowed lawn, a basketball hoop in the driveway and a pool in the backyard.

It is not clear whether Pamela and Paul Gendron saw signs of their son’s slide into extremism. But the messages recount a disturbing episode at the Gendrons’ home in late March.

Walking into the garage one night, Payton Gendron found a feral cat attacking his own cat, he wrote. Gendron repeatedly stabbed the feral cat with a knife, then smashed its head on a concrete slab and finally chopped off its head with a hatchet, he wrote. He posted a photo of the gray-haired cat, decapitated and bloody on the ground, surrounded by wet leaves.

“I called my mom and she gave me a box and I dug a shallow grave in the backyard,” he wrote on March 25. “Honestly right now I don’t feel anything about killing that cat. I thought I would be in pain but I literally just feel blank.”

Discord, the messaging platform, said in a statement Tuesday night that Gendron wrote the messages on an “invite-only server” that was, in effect, a “personal diary chat log” that only he could see.

“Approximately 30 minutes prior to the attack, however, a small group of people were invited to and joined the server,” a Discord spokesperson said in an emailed statement. Before that, the statement said, no other people saw the messages on the private chat log.

In the messages, Gendron recounts tensions with Black students at school in his childhood. In sixth grade, he wrote, he was suspended for a day after a Black student accused him of calling her the n-word. The school system declined to release his disciplinary records to The Post, citing privacy requirements.

Gendron did not consider himself a true racist, he wrote in the messages, until 2020, when he began reading an anonymous Internet message board, 4chan, where users celebrate racist violence.

In June of last year, Gendron underwent a psychiatric evaluation after he said in an online high school class that he planned to commit “murder/suicide.” Gendron wrote that he was cleared after he told the evaluators he was joking to get out of class. “It was not a joke,” he said in the Discord messages. “I wrote that down because that’s what I was planning to do.”

Gendron had for years owned a Savage Axis XP bolt-action hunting rifle, a Christmas present from his father when he was 16, according to the messages. Under New York state law, it is legal to possess a long gun starting at age 16.

Starting in December 2021, Gendron wrote, he began buying more weapons, including the shotgun, a Mossberg 500, and the Bushmaster XM-15 semiautomatic rifle he allegedly used in the Buffalo attack. In New York state, customers ages 18 and older are allowed to buy rifles and shotguns without a permit.

Gendron’s parents thought he was attending classes this spring at SUNY Broome Community College, according to the messages. Instead, he spent his days preparing for the attack and working on a 180-page screed that laid out his racist views, the messages show. At one point, Gendron worried that a speeding ticket from one of his trips to stake out the Buffalo grocery store would tip off his parents to the ruse.

“I’m compromised guys!” he wrote on March 26. “I got mail … saying I was speeding in Groveland and now my dad knows I was hours away doing something I shouldn’t have.”

Gendron wrote that his parents confronted him later that week.

“I just had a meeting with my parents about everything that happened this week,” he wrote on March 29. “I lied nearly the entire time. I said I was doing fine in school and going to every class when I haven’t been in a class for weeks now.”

A spokeswoman for the community college said in a statement that Gendron’s enrollment officially ended on March 22. The school would not comment on Gendron’s attendance before then. But students typically must miss weeks of classes without explanation before the school moves them off the student rolls, said Kevin Drumm, the college’s president.

As Gendron’s plans came closer to being realized, he described feeling severed from his roots.

“I feel completely disconnected from my past,” he wrote on April 1. “It’s like I was reborn and was forced fed memories that I’m supposed to believe are connected to me but in reality it’s not.”

By late April, Gendron wrote that he was taking the final steps to prepare for the attack — but only at strategic times.

“I’m doing laundry … and moving stuff into my car,” he wrote on April 29. “I have to wait to move the guns because my mom is downstairs and I can’t let her see.”

“I shoud’ve kept all my illegal stuff and guns in my car just in case my parents or brothers wanted to snoop through my room, luckily they didn’t,” he added.

A little more than a week before the attack, Gendron reflected on his deceptions, grateful that his parents repeatedly gave him the benefit of the doubt.

“I lied to them for months now,” he wrote about his parents on May 5. “I’ve been lucky at manipulating their emotions to blame themselves for my strange behavior. If only they knew.”

Alice Crites, Emma Brown, Beth Reinhard, Jon Swaine and Dalton Bennett contributed to this report.