HARTFORD, Conn. (AP) -- A convicted murderer sentenced to more than a half-century behind bars is suing the state of Connecticut, saying its ban on pornography in prison violates his constitutional rights. Dwight Pink Jr., 44, says in the lawsuit filed in U.S. District Court in July that guards have used the policy to deny him an art book, "The Atlas of Foreshortening," which uses nude models to help show how to draw the human form. Pink says the ban is a violation of his free speech rights and serves no meaningful objective in prison. The state filed its response Monday, saying Pink has not been harmed by the ban and none of his rights were violated. "Any injury or harm, if any, was caused solely by plaintiff's own acts, omissions, or conduct and was not due to any wrongful conduct by the defendants," Assistant Attorney General Steven Strom wrote. The state Department of Correction put out the administrative directive in 2011. It bans all material that contains "pictorial depictions of sexual activity or nudity" from the prisons. But it also says the ban should not apply to "materials which, taken as a whole, are literary, artistic, educational or scientific in nature." A prison spokesman at the time said the ban was intended to improve the work environment for prison staffers, especially female staffers, who might be inadvertently exposed to pornography. It led to a letter-writing campaign and threats of lawsuits from inmates upset with the policy. Jaclyn Falkowski, a spokeswoman for the attorney general's office, said about a half dozen lawsuits have been filed since then challenging the ban in both federal and state courts. She said those cases are still being litigated. But a judge in 2012 refused to issue a preliminary injunction allowing inmate Akove Ortiz to possess magazines like "Playboy." "Although prisoners do not forfeit all of their constitutional rights upon incarceration, the fact of incarceration and the needs of the prison system impose limitations on prisoners' constitutional rights, even those derived from the First Amendment," the judge wrote in his ruling. William Dunlap, a law professor at Quinnipiac University, said courts have generally sided with prison officials in such cases if they can prove the ban has a legitimate goal other than to simply suppress material that some people might find objectionable -- such as maintaining safety in the prisons or keeping the material out of the hands of sex offenders. But he said the lawsuit has a chance of succeeding if Pink can show it was improperly used in his case to suppress art or literature. "I think that's a much stronger argument than saying the statute itself is facially unconstitutional," he said. Pink is serving a 56-year sentence for his part in the 1998 slaying of a 35-year-old father of two in Old Saybrook. Scott Rufin was shot up to five times in the head with two guns and stabbed in the heart seven times with a sword, authorities said. Pink led authorities to the skeletal remains two years after the killing, which he said was committed by another man.