(CNN) -- A single lethal injection was supposed to speedily end Joseph Wood's life last week. When it didn't, Arizona executioners gave him a total of 15 doses of a novel drug cocktail, according to prison documents released Friday. It took nearly two hours for Wood to die, as he gulped and snarled for air, journalists attending the execution said Wood, who was said to have assaulted Debbie during their relationship, walked into Dietz and Sons Auto Paint and Body Shop and shot 55-year-old Gene in the chest. Then, as a desperate Debbie tried to phone for help, Wood grabbed her round the neck. The Arizona Daily Star reports that witnesses heard him tell his her "I told you I was going to do it. I love you. I have to kill you, bitch before also shooting the 29-year-old fatally in the chest. When police arrived Wood turned his gun on officers, prompting them to open fire and shoot him nine times.