Philip Manshaus, a 21-year-old Norwegian man, murdered his 17-year-old adopted sister Johanne Ihle-Hansen at their home.

Manshaus was fixated on far-right conspiracy theories and mass shootings, and had been investigated in 2018 after a tip was filed over his neo-Nazi views.

Manshaus was convicted of murder and committing an act of terrorism, and in 2020 was sentenced to 21 years preventative detention, an order which, in Norway, can be extended indefinitely.

[2] Genocide: Massacres, torture, expulsion: Other incidents: Beginning in the summer of 2017, Manshaus had been interested in conspiracy theories.

His internet activity included him reading about school shootings in Finland and in the US; he was interested in "alt-right" and neo-Nazi materials online, reading among others the works of Jordan Peterson, James Mason's Siege, and the manifesto of Norwegian terrorist Anders Behring Breivik.

[5] On 18 June 2018, a tip about Manshaus was sent to the PST, the domestic intelligence service in Norway, stating that he had far-right views and that his friends called him a neo-Nazi.

[2] In the weeks before the attack, Manshaus tried to join the neo-Nazi Nordic Resistance Movement, but due to an internal split in the organization and delays in their membership system he never got beyond the first of two planned initiation interviews.

[2] On 15 March 2019, Brenton Tarrant committed an anti-Muslim terrorist mass shooting in Christchurch, New Zealand, killing 51 people and livestreaming the attack.

[21][17] After Manshaus read it, it deeply affected him, and he slept and ate little for several days; he viewed it as a "call" for him to "take action".

[23] Manshaus's family noticed he had attached newspaper clippings about the Christchurch mosque shootings, a swastika, and information on other terrorist attacks to his wall, and hid it behind a Norwegian flag, after which Ihle-Hansen became afraid he would hurt someone.

[2] The day before her murder, she texted her boyfriend and expressed frustration with Manshaus's racist views, and told him that his room was full of "Nazi propaganda and newspaper clippings about mass shootings".

[24][25] He then loaded one of the rifles and walked into Ihle-Hansen's bedroom, before 3 p.m.[25][2] After an initial misfire, he shot her three times in the chest and once in the head; she died instantly.

[28] Manshaus brought with him to the mosque several weapons and a large quantity of ammunition, as well as body armor and a helmet.

[33][34] He also brought a computer and a phone which he used to attempt to live stream the shooting on Facebook with a GoPro camera attached to his helmet.

[33][3][17][20] When Manshaus entered the mosque, prayer had already ended and most had already left the building, leaving only a few elderly members of the congregation.

One of the men, Mohammad Rafiq, approached the gunman and pinned him down, moving Manshaus's weapons away after he dropped them.

[36][39][38] He received minor injuries while the perpetrator tried to break free from a chokehold, including an attempt to gouge out Rafiq's left eye.

[44] Another worshipper, Irfan Mushtaq, came to the mosque and helped restrain Manshaus by tying his legs together using the imam's shawl.

[39] Norwegian police stated the day after the arrest that they were planning to give the perpetrator a mental health assessment.

[5] The prosecution called the murder of Ihle-Hansen an "outright execution" and said Manshaus had showed "no mercy" in court, arguing for the maximum sentence of 21 years preventative detention (which means that he will be imprisoned indefinitely if he continues to be a threat to society).

[4] In addition to his sentence, Manshaus was ordered to compensate his victim's families and pay their legal fees of 100,000 NOK (~US$9,000).

[52] While imprisoned, Manshaus gave an interview in a documentary series about the case, Brennpunkt: Philips vei til terror, where he attributed his radicalization to the internet, stating:[54] There are a lot of different ways to get the views I have, which are quite different from the normal.

Some people for example read books, for example Mein Kampf, or another fascist literary work, and then in a period of maybe 5–15 years come to a conclusion that things may not be as they were brought up to believe.

[2] After her murder, there was increased media attention paid to the status of international adoptees in Norway, which were noted as an "invisible minority" group.

[61] Solberg and Abid Raja, a Liberal Norwegian politician, spoke together on the day of the attack, assuring the public that places of worship should be safe and calling for plans to break down Islamophobia in the country.

[40][64] Criticism of the right-wing Progress Party's rhetoric resurged after the shooting, due in part to their usage of the phrase snikislamisering (transl.

Prime minister Solberg and other important official figures, as well as the large Numbers of the Muslims attended an EID Pryer.

Other religioun leaders, Community members were present at the spot to show their solidarity held in Sandvika.

[75][76] The same year, journalist Anne Bitsch wrote Den norske skyld: En beretning fra rettssaken mot Philip Manshaus (transl.

[78][79][20] Manshaus himself was referenced in the writings of Payton Gendron, the perpetrator of the 2022 Buffalo shooting, who also wrote his name on one of the guns used in the attack.