The Islamic Central Council of Switzerland claimed the attacker was motivated by anti-Muslim sentiment, though this was questioned by the gunman's family.

[1] The police identified a suspect in the murder the next morning based on DNA evidence at the scene, and began searching for the assailant.

[3][14] The man responsible for the murder and subsequent shooting was identified as Manuel O.,[6][10] a 24-year-old Swiss citizen of Ghanaian descent living in Uster.

[4] Evidence in his apartment and statements from his family indicated he had had a substantial interest in occult practices and Satanism since his youth, but the motivation for both the stabbing death and subsequent shooting was unclear.

[1][6] He was interested in conspiracy theories and the end of the world, and had a room in his apartment dedicated to occult rituals, which he would not let anyone, even his mother, enter.

After the annexation of Crimea in 2014, he became afraid of the outbreak of World War III, and urged his family to stock up on emergency supplies.

[6] Relatives noticed his condition became worse in the summer of 2016: he lost his job, didn't pay the bills, would not answer calls, and seemed to retreat into himself.

[12] Police indicated that there was no evidence that the suspect was connected to either Islamist or right-wing extremists, and that it was unclear if he was mentally ill.[1][15] Other than an arrest for stealing a bicycle seven years before the shooting and juvenile charges for assault, the perpetrator had no criminal record.

[15] As the shooting at the Islamic center occurred on the same day as the assassination of Andrei Karlov and the 2016 Berlin truck attack, there was initially fear that the events might be related.

[16] American President-elect Donald Trump called all three events "terror attacks" and said that "the civilized world must change thinking".

[19] They encouraged mosques and Islamic institutions to be vigilant against the threat of violence and called on federal and cantonal authorities to guarantee the security of Switzerland's Muslim minority.