EDITORS PLEASE NOTE: THIS EDIT CONTAINS MATERIAL WHICH WAS ORIGINALLY 4:3br br Although actor Philip Seymour Hoffman was found with a syringe in his arm, the cause of his death remains undetermined and more study is needed, according to New York City's Chief Medical Examiner .br br Four people were arrested on Tuesday during a raid on a building in lower Manhattan after police traced what they believe to have been the source of the heroin suspected of killing the Oscar-winning actor.br br Meanwhile, Hollywood continues to mourn of the loss of Hoffman, one of the leading actors of his generationbr br At the world premiere of "The Monuments Men," actor George Clooney said he was filled with both shock and sorrow upon hearing the news.br br SOUNDBITE George Clooney saying (English):br br "It's very difficult and very tricky to be here tonight in this town, you know, two days after he, you know, he's gone," said a subdued Clooney.