Federal prosecutors have accused a Chicago man of obstruction of justice for allegedly deleting the encrypted messaging application Signal from his phone after being questioned about his role in the "planning of a violent attack" targeting the recent Ultimate Fighting Championship event at the White House on President Donald Trump's birthday.Alexander Iniguez Mercado, 20, faces up to two decades in prison if convicted of the charge in a one-count grand jury indictment made public Friday. He was set to appear before a federal magistrate judge later Friday afternoon.The news comes as U.S. Attorney Andrew Boutros faces controversy over how his office has secured indictments from grand juries. That scandal has mostly revolved around a single prosecutor, though.The FBI "obtained information" that Mercado "was a member and an administrator" of Signal messaging groups that included people who appeared to be communicating about the planned attack on the June 14 event, according to the indictment.An FBI special agent spoke by phone with Mercado on June 13, the indictment says. When the agent asked if Mercado planned to travel to Washington, D.C., to help with an attack, Mercado allegedly denied it and said he did not want to meet. The call was disconnected "after a brief conversation," the indictment alleges.Mercado also allegedly did not "initially respond" to another attempt by the agent to set up an interview. Mercado allegedly uninstalled Signal from his phone between June 13 and June 14. At least seven others have been charged in the alleged plot.This is a developing story. Check back for updates. ...read more read less