Tokyo , Japan ( CNN ) -- Anti-whaling activist Peter Bethune testified in a trial Monday that he had no intention of hurting anyone when he protested Japan 's whale hunt . The New Zealand activist from the Sea Shepherd Conservation Society , standing trial in Tokyo District Court , said that he believed bottles of butyric acid he threw at the Shonan Maru 2 whaling ship were non-toxic and would not harm anyone . Bethune faces five charges , including assault against whalers and trespassing into a whaling vessel . He pleaded guilty last week to all charges but assault . If convicted , Bethune faces a maximum of 15 years behind bars . At Monday 's hearing he tearfully described the January collision between the Shonan Maru 2 and the Sea Shepherd 's multi-million-dollar speedboat , the Ady Gil . The crash sunk the Ady Gil , which Bethune captained . 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 last week , 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 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 has claimed the science argument is a sham , noting that the whale meat then gets sold in Japanese markets and served in restaurants . A verdict is expected June 10 . CNN 's Yoko Wakatsuki and Junko Ogura contributed to this report .
Anti-whaling activist facing charges of assault , trespassing . Peter Bethune says he did not intend to harm anyone . Bethune admits he threw butyric acid at Japanese whaling ship . Activists were protesting Japan 's whale-hunting practices .