There is no evidence the Sept. 11 attack on the U.S. Consulate in Benghazi was planned "days or weeks in advance," a U.S. official told the Los Angeles Times. The attack, in which U.S. Ambassador Christopher Stevens and three other Americans were killed, appears to have been a case of opportunism, and intelligence agencies have found no evidence connecting it to al-Qaida, the newspaper reported Friday, citing U.S. officials and witnesses interviewed in Libya. A U.S. intelligence official who requested anonymity told the Times the attack was "carried out following a minimum amount of planning." "The attackers exhibited a high degree of disorganization," the official said. "Some joined the attack in progress, some did not have weapons and others just seemed interested in looting." "There isn't any intelligence that the attackers pre-planned their assault days or weeks in advance," another official said, adding most of the evidence to date indicates "the attackers launched their assault opportunistically after they learned about the violence at the U.S. Embassy in Cairo" earlier in the day. The violence at the Cairo embassy was associated with protests of a video made in California that Muslims found offensive for its portrayal of the Prophet Muhammad. Rep. Darrell Issa, R-Calif., chairman of the House Oversight and Government Reform Committee, wrote an open letter to President Barack Obama Friday, demanding answers about the attack. "Americans ... deserve a complete explanation about your administration's decision to accelerate a normalized presence in Libya at what now appears to be at the cost of endangering lives," Issa wrote. "These critical foreign policy decisions are not made by low- or mid-level career officials -- they are typically made through a structured and well-reasoned process that includes the National Security Council at the White House." The Senate Intelligence Committee's seven Republican members also wrote a letter to Obama, demanding to know who leaked information about a possible retaliation for the Libya attack, The Hill reported Saturday. "It seems counterintuitive to broadcast our intent to take action," they wrote, "as that would certainly give those responsible for this terrorist attack a chance to take evasive measures."