Tokyo , Japan ( CNN ) -- Wearing a dark , Japanese style business suit , New Zealand environmental activist Peter Bethune sat in-between two uniformed court officers as his trial began on Thursday in downtown Tokyo . The officers stared ahead , unflinching , as 44-year-old Bethune scanned the courtroom . The head judge ran through each of the charges in Japanese . When the court interpreter began translating into English , Bethune turned to listen . The charges are serious , announced the court : trespassing , damage to property , assault , forcible obstruction of official business and possession of an illegal knife . If convicted on all counts , Bethune faces a maximum of 15 years behind bars . Bethune was captain of Sea Shepherd 's futuristic boat , the Ady Gil . The batmobile-esque , $ 3 million boat collided with a Japanese whaling ship , the Shonan Maru 2 , and sank in January . Weeks later , Bethune jumped aboard the Shonan Maru 2 and attempted to make a citizen 's arrest of the captain . He was arrested and brought back to Japan to face criminal charges . In court Thursday , Bethune admitted to all the charges , except for assault . `` I admit that I boarded the Shonan Maru , but I believe that I have good reason to do so , '' he said . `` I admit that I fired the butyric acid , but there were additional circumstances that we will discuss in court . '' Prosecutors say the butyric acid burned two crew members of the Japanese whaling fleet , but Sea Shepherd calls it a harmless , albeit rancid , liquid . Butyric acid is found in rancid butter and vomit . Bethune 's Japanese attorneys have mounted a defense on the assault charge , which will be fought out until the trial ends on Monday . Bethune 's case is the first time a Sea Shepherd activist has been tried in a Japanese criminal court in the group 's long-running battle with Japan 's whalers in the icy waters of the Antarctic . Japan annually hunts whales in the Antarctic , despite a worldwide moratorium on whaling , under the loophole that a country may legally do so if its purpose is scientific research . Sea Shepherd , who notes the whale meat then gets sold in Japanese markets and served in restaurants , calls the science argument a sham . Sea Shepherd 's Seattle-based attorney , Dan Harris , is in Tokyo for Bethune 's trial , though he is not Bethune 's official Japanese counsel . `` This whole trial has been brought about for political reasons , far more than criminal reasons . If you look at what Peter Bethune did , he did n't do anything , '' Harris said . `` He climbed aboard a Japanese ship . Nobody was in any danger . No one was under any threat . No one was afraid . For Japan to act like it 's enforcing a criminal law is a little disingenuous , when you look at what Pete Bethune did . '' Japan maintains that when its laws are broken , it will prosecute . `` We all recognize the right of protest , right of demonstration , right to express their views . That does not mean you can attack people with force , attack our vessels and crews with their vessels , '' said Joji Morishita , from Japan 's Fisheries Agency . Bethune testifies on Monday . A verdict is expected on June 10 .
Charges against Peter Bethune include trespassing . The charges were filed in the U.S. District Court for the Eastern District of New York. Verdict is expected on June 10 .