The Kingdom of Saudi Arabia sent a written warning about accused Boston Marathon bomber Tamerlan Tsarnaev to the U.S. Department of Homeland Security in 2012, long before pressure-cooker blasts killed three and maimed hundreds, according to a senior Saudi government official with direct knowledge of the document. The Saudi warning, the official told MailOnline, was separate from the multiple red flags raised by Russian intelligence in 2011, and was based on human intelligence developed independently in Yemen. Citing security concerns, the Saudi government also denied an entry visa to the elder Tsarnaev brother in December 2011, when he hoped to...