A man was fatally stabbed aboard a Chicago Transit Authority Blue Line train as it travelled through Des Plaines on Wednesday night, local authorities said. Emergency responders were called after reports of a knife attack on the north-west suburban route, but the victim could not be saved. Des Plaines police opened a homicide investigation and worked with transit security officers to collect video evidence and interview riders. Officials described the assault as an isolated incident and said no other passengers were physically injured. Two days later, on Friday, police arrested and charged a suburban man in connection with the killing. Investigators have not released the names of either the victim or the suspect, nor given details on a possible motive. The suspect remains in custody as prosecutors prepare to present the case in Cook County court.