A First Officer reports finding an unidentified metal tool on the aft side of #2 engine N1 fan blades extending between the stator blades; during a pre-flight walkaround of a B767-300 ETOPS aircraft.

Narrative

Upon arrival at gate I noticed aircraft had red beacon on. After completing my initial flow for preflight; I noticed an ETOPS release in ACARS; shutoff the red beacon and went outside to preflight. While inspecting the #2 engine from aft; I noticed an oblong object resting behind the #2 engine N1 blades extending between the stator blades. I discontinued prefight and called Maintenance Control. Mechanics arrived shortly and removed what they described as an extension bar.The aircraft had been towed to the gate from the ramp for our flight. I do not know if the tool in question was left after a maintenance issue; whether or not the tool in question was part of the tool control program; or the extension bar in question was left deliberately as an act of sabotage.Certainly if this so-called extension bar is part of the tool control program the appropriate authority needs to investigate why the tool was not reported missing. If the extension bar is not part of the program and is a necessary device; perhaps consideration should be made to including this type of tool in the control program. If this was a deliberate act of sabotage; law enforcement should be involved.