DALLAS—A Texas judge declared a mistrial Friday in the first murder case against a man charged with killing 18 older women in the Dallas area over a two-year span. Judge Raquel Jones issued the ruling when a jury deadlocked after deliberating since Thursday afternoon in the capital murder case charging Billy Chemirmir with the death of 81-year-old Lu Thi Harris. The mistrial raises questions about how prosecutors will proceed with the cases against Chemirmir, who authorities have accused of being a prolific killer preying on the elderly. The Dallas County District Attorney’s office did not immediately respond to a request for comment. In a series of notes to the court Friday, the 12 jurors said they were “hopelessly deadlocked 11 to one” over the case. It was not clear what verdict the majority of jurors supported. Jones initially resisted declaring a mistrial, repeatedly ordering the jury to continue deliberation. After …