Family members say that Esteban Santiago, the suspect in the Fort Lauderdale airport shooting in which five people were killed, seemed troubled when he came back from military service in Iraq. His brother described him as “more furious” after his deployment in 2010 with a Puerto Rico National Guard unit. His aunt said that after coming home, Mr. Santiago “lost his mind.”

After Mr. Santiago’s arrest in the shooting, emerging details of his military service led some to blame the rampage on the war-torn mind of a veteran haunted by post-traumatic stress disorder, a common pattern when veterans are arrested in violent crimes. But experts not connected to Mr. Santiago’s mental health treatment say it may be a mistake to blame PTSD. Mr. Santiago, who served for eight years in the National Guard and Army Reserve and saw combat in Iraq in 2010, exhibited symptoms that do not appear to fit the disorder, they say, and more closely resemble schizophrenia, a condition unrelated to military service.

Mr. Santiago’s family said he reported hearing voices and had other hallucinations, but said he was never given a diagnosis of PTSD. In November, he walked into an F.B.I. office in Alaska and told agents that his mind was being controlled by a United States intelligence agency.

“The delusions, the hallucinations are far more consistent with psychosis than PTSD,” said Dr. Donald C. Goff, a psychiatrist at New York University and a leading expert on schizophrenia. “So is the timing of the onset.”