The United States said Wednesday it was sending a team of investigators to help determine why a Yemeni man opened fire on oil workers, killing an American, a Canadian and a Yemeni before committing suicide. The Yemeni Interior Ministry said the motive in Tuesday’s attack was believed to be personal. The assailant, identified as Naji Abdullah al-Kumaim, had worked for the oil rig’s owner, Nabors Drilling Co., for seven years and suffered from depression, it said. Al-Kumaim was not known to have a political affiliation, and he shouted during the shooting that was taking revenge against people who were filing reports about him, the ministry said. The attack occurred at an oil field in the northern province of Marib, about 100 miles northeast of the Yemeni capital San`a. Full Story