[3] According to Rockland County Senior District Attorney Michael Dugandzic, police found the suspect with blood on his clothes and smelling "strongly" of bleach.
[15] Investigators found handwritten journals expressing antisemitic views, including material about Adolf Hitler, "Nazi culture", and drawings of a Star of David and of a swastika among Thomas's possessions.
[17] On the Saturday before the attack, the suspect's mobile browser was used to access an article titled "New York City Increases Police Presence in Jewish Neighborhoods".
[16] In recent weeks, Thomas had searched online for phrases such as "Why did Hitler hate the Jews" multiple times, as well as "German Jewish Temples near me".
[16] Thomas is also under investigation on suspicion of having committed a previous stabbing attack on an Orthodox Jewish man on his way to the early prayer service at 5:30 a.m. on November 20, 2019; the victim was critically injured.
[13] He had been diagnosed with paranoid schizophrenia in 2018, when he underwent a psychiatric evaluation at the Orange County Medical Center after being arrested for confronting a police officer with a knife.
[22] In March 2020, after 72-year-old Rabbi Josef Neumann died from his wounds three months after the attack, the Rockland County District Attorney announced that it would seek a grand jury indictment against Thomas for second-degree murder.
[23] Separately, on December 30, 2019, the U.S. Attorney's Office for the Southern District of New York filed a criminal complaint charging Thomas with five counts of "obstruction of free exercise of religious beliefs involving an attempt to kill and use of a dangerous weapon, and resulting in bodily injury" (a federal hate crime).
[25] Since that time, Thomas has mostly been detained at the Medical Center for Federal Prisoners in Springfield, Missouri,[13][26] although he has been transferred to a New York facility ahead of court proceedings there.
[13] On January 17, 2024, Rockland County Judge Kevin Russo ordered Thomas to be held at Mid-Hudson Forensic Psychiatric Center for up to two additional years.