CNN  — 

Social media posts by the 18-year-old White man suspected of shooting and killing 10 people at a Buffalo supermarket Saturday reveal he had been planning his attack for months.

Alleged gunman Payton S. Gendron of Conklin, New York, posted that he selected a particular ZIP code in Buffalo because it had the highest percentage of a Black population close enough to where he lived. Police and other officials have described the mass shooting as a hate crime.

In his posts, initially written on the chat app Discord and shared on online forum 4chan, the suspect said he visited the Tops Friendly Markets store three times on March 8 to survey the layout, as well as at the times of the day when there were the most customers. He planned his attack for mid-March, the posts say, but postponed it several times.

Of the 13 people shot, authorities say, 11 were Black. The alleged gunman was taken into custody in the immediate aftermath and is under suicide watch after pleading not guilty to a first-degree murder charge, according to authorities.

The 10 people killed ranged in age from 32 to 86, police said, among them a former police officer who tried to stop the gunman and a number of people doing their regular grocery shopping.

Here are the latest developments:

• Presidential visit: In Buffalo on Tuesday, President Joe Biden called the shooting “domestic terrorism – violence inflicted in the service of hate and the vicious thirst for power that defines one group of people being inherently inferior to any other group.” He said that people “need to say as clearly and as forcefully as we can that the ideology of White supremacy has no place in America.” He and first lady Jill Biden also visited a memorial site for the victims.

• Suspect visited supermarket the day before attack: Gendron was at the Tops store on Friday, the day before the shooting, “doing reconnaissance,” police Commissioner Joseph Gramaglia said. He was also in the city in early March, Gramaglia said.

• Manager says she told Gendron to leave: An operations manager at the market told ABC News that she saw him at the store on Friday evening and told him to leave because it looked like he was bothering customers. Gendron, sitting on a bench outside the store wearing the camouflage he would wear Saturday, left without an argument, Shonnell Harris Teague told ABC. Teague’s brother, the Rev. Tim Newkirk, told The Buffalo News that Gendron was “posing as a beggar,” and Teague told him he couldn’t panhandle there.

• Attack would have continued elsewhere had suspect not been stopped: The suspect had other “target locations” down the street, Erie County Sheriff John Garcia said. Authorities found another rifle and a shotgun in his vehicle, said Garcia, who credited the quick arrival of two police officers with preventing other attacks.

• Writing seen on suspect’s firearms: CNN has obtained a photo of two of the firearms inside the alleged gunman’s vehicle that were not used in the shooting. Writing is seen on the weapons, including the phrase “White Lives Matter,” as well as what appears to be the name of a victim of a crime committed by a Black suspect.

• Video shows gunman apologizing, sparing one person’s life: Video obtained by CNN and filmed during the shooting shows the gunman turning his weapon on a man who is curled up on the ground near what looks like a checkout lane. The man shouts, “No,” and the shooter then says “Sorry,” turns and walks away. The video ends at this point and it is unknown what happened next. It’s not clear why the man was apparently spared or why the gunman apologized.

President Joe Biden and first lady Jill Biden came to the scene Tuesday to pay respects and speak to families of the victims.

State police didn’t ask for ‘Red Flag’ order

Since the shooting, officials have looked at what they say was the suspect’s racist intent and his history.

The massacre follows other mass shootings in recent years in which authorities say a White supremacist suspect was motivated by racial hatred, including in El Paso, Texas, Charleston, South Carolina, and as far as Norway and New Zealand.

New York State Police officials did not seek a “Red Flag” order of protection against Gendron after responding to a call to a high school about a threatening statement, a state police spokesman told CNN on Tuesday.

Gendron had turned in a high school project about murder-suicides, Garcia, the Erie County sheriff has said. The Susquehanna Valley Central School District referred to it this week as an “ominous” reference to murder-suicide through a virtual learning platfo