WASHINGTON ó Defense Secretary James N. Mattis, troubled by a lack of information two weeks after an ambush on a special operations patrol in Niger left four U.S. soldiers dead, is demanding a timeline of what is known about the attack, as a team of investigators sent to West Africa begins its work.The growing list of unanswered questions and inability to construct a precise account of the Oct. 4 incident has exacerbated a public relations nightmare for the White House, which is now embroiled in controversy over President Donald Trumpís belated and seemingly clumsy response this week to console grieving military families."We need to find out what happened and why," White House Chief of Staff John F. Kelly, whose son was killed in Afghanistan in 2010, told reporters at the White House on Thursday.At the Pentagon, Mattis suggested to reporters that he would say little pending results of the investigation. "We at the Department of Defense like to know what weíre talking about before we talk," he said. "And so we donít have all the accurate information yet. We will release it as rapidly as we get it."The attack, apparently carried out by armed militants affiliated with the Islamic State, was the deadliest since Trump took office, yet the U.S. militaryís Africa Command still does not have a clear "story board" of facts that commanders usually gather swiftly after deadly incidents. That has senior Pentagon officials and lawmakers suggesting incompetence.The questions arising from the incident, particularly about the availability of additional military support to the patrol, echo those raised in the aftermath of the 2012 Benghazi attack in Libya, which resulted in the deaths of four people: U.S. Ambassador J. Christopher Stevens, foreign service information officer Sean Smith, and CIA contractors Glen Doherty and Tyrone Woods.Sen. John McCain, an Arizona Republican and chairman of the Senate Armed Services Committee, said on Thursday that getting to the bottom of what happened may require subpoenas."Thatís why weíre called the Senate Armed Services Committee," he said. "Itís because we have oversight of our military. So we deserve to have all the information."