A Norwegian man named Philip Manshaus was arrested on Saturday after waving a weapon and firing several shots inside a mosque in Baerum, Oslo.

Believed to have been inspired by white supremacists in the U.S. and New Zealand, the 21-year-old also became the main suspect in the killing of his stepsister, who was found dead in their home.

The victim, later identified as 17-year-old Johanne Zhangjia Ihle-Hansen, was adopted from China at the age of 2, reports KTLA.

According to security experts, Manshaus is an extremist who was radicalized by far-right conspiracy theories on the internet. One popular theory among supremacists is the “great replacement,” which believes that a “genocide” where white people are being replaced by immigrants and Muslims is taking place.

Experts say Manshaus emulated attacks when he entered the mosque, where three men were preparing for Sunday’s Eid al-Adha Muslim celebrations. After firing several shots, he was wrestled by a 65-year-old retired Pakistani Air Force officer who managed to take away his guns. Along with the others inside the Al-Noor Islamic Center, the elderly man reportedly held the suspect down until police arrived, preventing anyone from getting shot.

A subsequent raid in Manshaus’ nearby house led to the discovery of the dead body of his stepsister, police records revealed. Certain details such as the type of weapon used or other information about the alleged killing have not been revealed to the public.

Hans Sverre Sjoevold, head of Norway’s domestic security agency PST, revealed that while authorities already received a “vague” tip a year ago about the suspect, it was not acted upon due to the lack of information on any “concrete plans” of an attack.

Sjoevold explained that having a violent mindset does not necessarily mean the person would act on such inclinations. He further pointed out that capturing and preventing those who “have the ability and will to carry out attacks” will be a “demanding mission.”

However, local media reported that two recent high-profile shootings most likely inspired Manshaus to act. Norwegian newspaper Dagbladet pointed out that Manshaus was emboldened by the Christchurch mosque shootings in New Zealand in March that left 51 people dead, and the recent attack on El Paso, Texas, where an assailant left at least 22 dead.

On the day of the Oslo attack, Manshaus allegedly wrote online that he had been “chosen” by “Saint (Brenton) Tarrant,” the Christchurch mosque shootings gunman.

During a hearing on Monday, Manshaus entered a court in Oslo with a smirk on his face which noticeably still bore dark bruises under both eyes and scratches on his face and neck.

Manshaus’ lawyer, Unni Fries, told the Associated Press that the suspect did not admit guilt during the closed-door meeting and asked to be set free.

Under the court’s orders, Manshaus is to be held in pre-trial detention for four weeks, two of which will be spent in solitary confinement.

Featured Image via YouTube / Euronews