A fourth explosion in less than a month has hit Austin, Texas , with police hunting for what they believe to be a "serial bomber" or bombers with all of the incidents believed to be linked. Police said that the cause of the latest explosion is believed to have been triggered by a tripwire in the Travis County neighbourhood of the city. Police have appealed for video surveillance footage from residents and called on them to stay clear of any suspicious packages. They have also called on all those in the areas to stay in their homes so the scene of the Sunday night blast can be fully investigated. The two victims of the latest explosion are two white males, in their 20s who are being treated for non-life threatening injuries. Austin Police Chief Brian Manley asked the city “to have an extra level of vigilance and pay attention to any suspicious device whether it be a package, a bag, a backpack, anything that looks out of place and do not...