INDIANAPOLIS (AP) — An autopsy on a teenage shoplifting suspect who died in Indianapolis police custody after complaining of breathing problems found he suffered a heart attack.

The Marion County Coroner’s Office said Monday an autopsy on 18-year-old Terrell Day of Indianapolis determined his cause of death to be acute myocardial infarction, or a heart attack.

After Day was arrested Saturday afternoon for shoplifting on Indianapolis’ far east side, he told officers while in the back of a jail wagon that he was having trouble breathing.

Emergency workers were called. Day died in the back of an ambulance.

Officers were called to a clothing store after a security guard reported that a gun-wielding man accused of shoplifting had fled the business.

Police say they found Day in a grassy area near a handgun.