The tip came from a coworker. A 19-year-old in the Chicago suburb of Palatine was arrested on Sunday after someone who received “concerning electronic communications” from him went to the police, and by Wednesday officers said they had uncovered a document espousing white supremacist views and outlining a plan for a mass shooting, potentially targeting a Hindu place of worship in the Aurora area, Al Jazeera reported.

The accused is Alexandros Paporakis, 19, of Palatine. The chain of events, as described by Palatine police and reported by CBS Chicago, ran tip-to-arrest in a matter of hours: on Sunday afternoon, Mount Prospect police contacted Palatine police after being alerted by the message recipient; that evening, Paporakis was arrested outside his home on North Baldwin Court by Palatine and Mount Prospect officers.

The timing police described is the part that matters. “Based on information developed during the investigation, detectives believe Paporakis may have been planning to carry out an attack on Sunday, October 11, potentially targeting a Hindu place of worship in the Aurora area,” the Palatine police update read, as quoted by ABC7 Chicago. “However, the specific intended location has not been confirmed and remains under investigation.” If that reconstruction holds, the arrest came the same day as the alleged intended attack. Paporakis has been charged with making a terrorist threat.

Two qualifications belong on the record. First, the document’s contents and the attack plan are police characterisations of evidence, not yet findings tested in court; a manifesto expressing extremist ideology and discussing violence is what investigators described, but “may have been planning” is the operative phrase in their own statement. Second, it was not immediately clear whether Paporakis had legal representation, so no defence response exists yet.

The arrest came down to one person reading a disturbing message and making one phone call. Planned attacks are rarely interrupted so cheaply; whether the plot was days from execution or a fantasy typed into a document is now a question for the Cook County courts to answer from the seized communications.