NEW YORK—IRS Special Agent Gary Alford showed a jury personal e-mails from Ross Ulbricht's Gmail account that prosecutors say line up with chats and other records from the Silk Road drug-trafficking site. In 2013, Alford searched through the Gmail account belonging to Ulbricht, the 30-year-old Texan who stands accused of being the mastermind behind the Silk Road drug-trafficking website.