The FBI issues a bulletin to state and local law enforcement agencies which states that terrorists may use cultural, artistic or athletic visas to slip into the United States undetected. This is followed by another bulletin one day later from the FBI and Department of Homeland Security warning of pending terrorist attacks on buses and trains in major cities during the summer. The uncorroborated intelligence cited by the warning indicates the possible use of a bomb made out of ammonium nitrate fertilizer and diesel fuel, similar to the one used in the Oklahoma City federal building attack. This intelligence, as well as the March 11, 2004, train bombings in Madrid (see 7:37-7:42 a.m., March 11, 2004), reportedly increases the level of concern that terrorists are planning an attack in the US. It is reported that the intelligence community believes that al-Qaeda has the full intent and capability to execute coordinated and deadly attacks on public transportation systems. [PBS, 4/2/2004] No such attacks occur. The warning apparently is given because a number of suspects are arrested in Britain who had been working on a fertilizer bomb, but they have been under surveillance and their fertilizer had been replaced with a harmless substance. In the thousands of hours of monitored conversations, none of them mentioned anything about bombing the US (see Early 2003-April 6, 2004). One day prior to the first alert, Charles Duelfer, the chief weapons inspector in Iraq, informed Congress that no WMD have been found to date. [MSNBC, 6/4/2007]