A federal judge directed that an anonymous jury be seated in the racketeering trial of four purported street gang members who face the possibility of spending the rest of their lives in prison if convicted.In a written opinion Tuesday, U.S. District Judge Thomas M. Durkin of the Northern District of Illinois granted prosecutors’ unopposed motion to allow members of the jury pool summoned in the case to keep their identities secret.Withholding identifying information from the parties in a case helps protect members of the …