CINCINNATI—A judge has ordered a man accused of planning to kill sorority members at an Ohio university to remain behind bars. Magistrate Judge Stephanie Bowman on Friday cited a parole violation and the “serious nature of the charges” as reasons to keep 21-year-old Tres Genco in custody. The Hillsboro, Ohio, resident appeared in federal court in Cincinnati on charges of an attempted hate crime and possession of a machine gun. Federal prosecutors said earlier that Genco identifies himself as an “incel”—involuntary celibate—and has interacted with an online community of mostly men who advocate for violence against women because they believe they are unjustly denied sexual or romantic attention. Prosecutors allege that Genco conducted surveillance at an Ohio university in January 2020, described a document he wrote as “the writings of the deluded and homicidal” and signed it “Your hopeful friend and murderer.” Local police searched Genco’s home in March 2020 …