The U.S. air marshal who housed Floridian George Zimmerman after he shot an unarmed black teen said on television his friend was innocent of murder. Mark Osterman and his wife, Sondra, were on the syndicated \"Dr. Phil\" show Tuesday, promoting their book, \"Defending our Friend: The Most Hated Man in America,\" The Miami Herald reported. Host and psychologist Phillip McGraw peppered Osterman with questions, intimating Zimmerman violated the basic tenet of neighborhood watch programs by carrying a gun and leaving his vehicle to follow a suspect. the Herald said. Osterman, 44, is the friend Zimmerman\'s wife, Shellie, called Feb. 26, when her Hispanic-American husband, a neighborhood watch volunteer in Sanford, shot 17-year-old Trayvon Martin. Zimmerman said he shot Martin in self-defense, citing Florida\'s \"stand your ground\" law. Osterman, a one-time Seminole County sheriff\'s deputy, went to the scene, was with Zimmerman during police interrogations and housed the Zimmermans for more than a month after a national furor arose in the matter. Osterman said Zimmerman was \"heartbroken and devastated\" about the killing, adding that his friend sustained a concussion and likely would not have survived had he not used lethal force. \"There is no upside to this,\" Osterman said on the show, adding that he helped pick out the gun used in the shooting. \"From what George told me, he believes he would not be alive today if he had not done that. ... According to what he told me, there was no time to think.\" While Osterman suggested he wrote the book as a fundraising effort for Zimmerman, the defense legal team said via Twitter the plan wasn\'t approved by the defense. \"Osterman\'s book and TV spot, although well-intentioned, are ill-timed and done without input and NOT approved by the defense,\" the legal team wrote it its Twitter account. Martin\'s stepmother, Alicia Stanley, also appeared on \"Dr. Phil.\" \"You sit here like you were proud: \'I picked that gun out,\'\" she said. \"Why would you want people to know that? I know he\'s your friend, but that don\'t mean he\'s not a liar.\" Prosecutors have charged Zimmerman with second-degree murder.