SEATTLE — A lawyer for an American soldier set to be sentenced for killing 16 Afghan civilians may cite a new Food and Drug Administration warning about the psychiatric side effects of an antimalarial drug used by U.S. troops.On Monday, the FDA said mefloquine — known as Lariam, its brand name — can cause long-term neurological damage and serious psychiatric side effects.Attorney John Henry Browne has said he has documents indicating his client, Staff Sgt. Robert Bales, took the drug while in Iraq, but medical records for his time in Afghanistan are incomplete. Browne told The Seattle Times the FDA warning was an interesting development.“We’re all over this,” Browne said.Bales pleaded guilty to the 2012 killings last month. A jury will decide in August whether the soldier is sentenced to life with or without the possibility of parole. Army officials have not commented on whether Bales took mefloquine in Afghanistan, citing confidentiality laws that protect a patient’s records.An Army sanity board already has concluded Bales suffered from no serious mental diseases or defects at the time of the killings, and that he could understand the court-martial proceedings that led to a plea agreement earlier this year. Bales, an Ohio native and father of two from Lake Tapps slipped away from his remote southern Afghanistan outpost at Camp Belambay early on March 11, 2012, and attacked compounds in nearby villages. Most of the victims were women and children, and some of the bodies were piled and burned. The slayings drew such angry protests that the U.S. temporarily stopped combat operations in Afghanistan.