MONTGOMERY, Ala.—Alabama would be the first state to carry out an execution this year if it proceeds with plans to put to death a 51-year-old inmate convicted of the shotgun slaying of a police detective’s sister decades ago. The 11th U.S. Circuit Court of Appeals issued a stay blocking the Thursday night execution, but the state is expected to appeal. Willie B. Smith III was scheduled to receive a lethal injection at a south Alabama prison for the 1991 murder of Sharma Ruth Johnson in Birmingham. Prosecutors said Smith abducted Johnson, 22, at gunpoint from an ATM, stole $80 from her and then took her to a cemetery where he shot her in the back of the head. Judges on the 11th Circuit stayed the lethal injection to give time to consider defense claims that the state failed to give the man, who has an IQ of below 75, required …