A Minnesota man who federal authorities say expressed admiration for mass shooters was arrested Wednesday after allegedly trying to purchase hand grenades and a firearm component that converts an AR-15 style rifle into an illegal machine gun, the Justice Department announced.River Smith, 20, has been charged with one count each of illegal possession of a machine gun and attempting to receive and possess destructive devices, according to a criminal complaint.During an FBI investigation, Smith told a government informant that he is “pro mass shooting.” He also expressed sympathy for the Parkland school shooter and called the person charged in the recent shooting at a Colorado Springs LGBTQ nightclub “a hero,” according to the complaint.Smith was reported to the FBI in September by a retired police officer who works at a gun range Smith frequented, according to the complaint.Over the course of the investigation, Smith told a confidential government source that he has an “intense dislike” of minorities, Jewish people and gay people and expressed racism toward Black people, according to the complaint."