 Complete the following phrase:  Wagner is believed to have a Serb unit, which was, until at least April 2016, under the command of Davor Savičić, a Bosnian Serb who was a member of the Serb Volunteer Guard also known as Arkans Tigers during the Bosnian War and the Special Operations Unit JSO during the Kosovo War. His call sign in Bosnia was Elvis. Savičić was reportedly only three days in the Luhansk region when a BTR armored personnel carrier fired at his checkpoint, leaving him shell-shocked. After this, he left to be treated. He was also reported to had been involved in 