Police are investigating online videos apparently posted by the shooter who killed two children and injured 17 other people at a Catholic church in Minneapolis, which describe an obsession with school shootings and show a rambling written statement and numerous guns painted with slurs, mass killers’ names and political messages.

Minneapolis police chief Brian O’Hara identified the suspected shooter as Robin Westman, who died from a self-inflicted wound after firing into Annunciation Catholic Church during a morning Mass.

Westman, 23, graduated from Annunciation’s grade school in 2017, according to a yearbook photo obtained by CNN.

Authorities are now evaluating a series of bizarre videos posted to YouTube by a user identified as “Robin W” to authenticate them and potentially learn more about the motivations in the attack, police sources told CNN.

The videos, which have been taken down, were uploaded on Wednesday (Thursday AEST).

O’Hara said the shooter had posted a “manifesto” that was timed to be published on YouTube, and that investigators were going through it to “try and develop a motive from that”.

In the videos, two of which were titled with Westman’s full name, the person recording the video pages through a handwritten notebook and displays a shooting target with an image of Jesus and a collection of guns, magazines and ammunition laid out on a bed.

Various messages and racial and religious slurs were written on the weapons, including “psycho killer” and “suck on this!”

Antisemitic messages were also scrawled on the guns, with one reading “6 million wasn’t enough”.

Another magazine had the message, “kill Donald Trump”.

In a voiceover of one video, the person filming also claimed to have met and to support Brandon Herrera, a pro-gun YouTuber who lost a Republican primary for a Texas congressional seat last year.

Herrera condemned the attack in a social media message posted on Wednesday afternoon, saying the shooter would “burn in hell.”

Another of the gun magazines shown in the videos lists the names of six notorious mass shooters, including Adam Lanza, whom the suspect wrote they had a “deep fascination” for.

Lanza gunned down 26 people – including 20 children – at Sandy Hook Elementary School in Connecticut in 2012.

The name of Robert Bowers, who was convicted of killing 11 people at a Pittsburgh synagogue in 2018, is also legible on the side of one of the weapons.

The rambling notebook – which was written partially in English and partially using English words in Cyrillic script with some Russian words – expresses feelings of self-hatred and wishes to die.

Other entries described the author becoming “morbidly obsessed” at a young age with Lanza and other past school shooters.

“I’m so sorry” is written in large letters on one page. The person filming whispered “I love my family” while recording that page, and said “I don’t know what else to say” at another point in the video.

The notebook also included a diagram of the inside of a church that seems to match the layout of Annunciation Church.

The person recording showed themselves stabbing a knife into the drawing while saying, “ha, nice.”

The writings in the notebook, along with images on the weapons, express a wide embrace of racism and antisemitic views – although the author claims those extremist ideas aren’t expressly the reason behind the attack.

“In regards to my motivation behind the attack I can’t really put my finger on a specific purpose. It definitely wouldn’t be for racism or white supremacy,” the notebook reads.

“I don’t want to do it to spread a message. I do it to please myself. I do it because I am sick.”

Cody Zoschak, a senior manager at the Institute for Strategic Dialogue, a research group that tracks extremism online, told CNN that the videos seemed similar to writings published by Solomon Henderson, who fatally shot a fellow student and injured one other person before killing himself at a Nashville high school earlier this year.

“He was associated with similar online subcultures and nihilistic violence; he had a very confusing mix of materials in his manifesto, and generally we saw a lot of efforts to misdirect and or troll,” Zoschak said.

The suspect’s last known address was at Westman’s father’s home about a 20-minute walk from Annunciation, on a quiet block of craftsman bungalows.

The elder Westman and a woman were seen by several neighbours sitting on the curb on Wednesday, looking stricken as law enforcement officers from various agencies went through their house.

Jim White, 57, who lives across the street, described them as a friendly couple who, when they learned White was working on a landscaping project, gave him hundreds of cement blocks to create a planter that now adorns his front lawn.

“They are very nice neighbours, very good people,” he said.

Neighbour Terry Cole said he didn’t remember seeing the suspected shooter often in the neighbourhood.

Cole briefly choked up while speaking with a CNN reporter.

“They are a wonderful couple — a good part of this neighbourhood,” he said. “People take care of each other here. It’s just such an absolute shock.”

The suspected shooter’s mother worked at Annunciation from 2016 through 2021, according to social media posts.

Westman attended the Minnesota Transitions Charter School for two months at the beginning of the 2017 school year, after graduating from Annunciation, a spokesperson for the charter school confirmed, but it’s unclear whether the suspect graduated from high school.

In 2019, the suspect’s mother filed to legally change the suspect’s name from Robert Paul Westman to Robin M. Westman, court documents show.

A judge who approved the petition in January 2020 wrote that the suspect “identifies as a female and wants her name to reflect that identification.”

A search of state court records showed no criminal history for Westman, but some traffic citations in 2021.