"Chief suspect" refers to the person who is believed to be most likely responsible for a crime or wrongdoing. They are the main person of interest in an investigation. Full definition
Douglas plays Nick Curran, recovering alcoholic SF police detective with a murky past; Sharon Stone is Catherine Tramell, the blonde bombshell chief suspect in his murder investigation. (clothesonfilm.com)
The Fire Chief suspects that the crew attempted to put the fire out, and that it's likely that they waited before they called 911. (effectivecoverage.com)
The one in the dark hat is «Suspect One» and the one in the white hat is «Suspect Two,» they're believed to be connected, and they're the FBI's two chief suspects in the Boston Marathon bombing case. (relevantmagazine.com)