ASHINGTON, Oct. 17 — Federal law enforcement authorities said in court documents unsealed on Friday that they suspected a group of Islamic charities in Northern Virginia of laundering hundreds of thousands of dollars or more from Saudi Arabia to help finance terrorist attacks by Hamas and other militant groups.The authorities said in documents that they suspected that the network of charitable and educational institutions known as the Saar group in Herndon, Va., used an elaborate system of domestic and overseas financial transactions to "blur the trail" of its revenues and disguise the fact that it was sending money to aid...