The FBI are yet to declare a motive but are believed to be investigating for links to terrorism. "There are many reports circulating, but the FBI deals only in facts," special agent Rachel Rojas told a news conference on Friday night. Saudi Arabia is a key US ally in the Middle East and the two countries have longstanding military exchange programmes. The shooting has already prompted questions about the vetting of foreign military personnel sent to the US for training. It is the second shooting to take place at a US military base this week. A US sailor shot dead two workers at the Pearl Harbor military base in Hawaii on Wednesday.