Behind the attacks. And of course the question that looms, is this the work of a serial bomber . Cnns ed lavandara is live in austin with the breaking details. Ed reporter good morning, erica. Authorities are waiting for the sun to come can up so they can begin processing the scene of this latest explosion. It happened last night. Two men in their 20s were injured. They are being treated in a local hospital. Not life atlantaing injuries. They are expected to be okay. This latest explosion a little bit different than the three previous we have seen since march 2nd. The three previous explosions taking place on the east side of the austin area. This particular location in southwest austin. So quite a ways away from where the previous explosions had taken place. Also, authorities believe that a trip wire is what detonated the latest explosion. That also very different from the other three explosions. That is why the police chief here in austin is telling residents across the city to be hi