You are right to say that the organization that was behind the assassination of Archduke Franz Ferdinand was called the Black Hand. It was they who sent a group of six people to try to kill the archduke in Sarajevo on June 28, 1914. The member of the group who actually killed the archduke that day was a young man (he was just short of his 20th birthday) named Gavrilo Princip. He was not the first one that day to try to kill the archduke. Others in the group tried, but it was Princip who actually succeeded.
Thank you soooo much :)