A B767 CREW; AFTER PARKING AT THE GATE IN DEN; EXITED THE ACFT LEAVING THE L ENG RUNNING.

Narrative

WE ARRIVED AT GATE IN DEN. SET PARKING BRAKE; SHUT DOWN R ENG; AND TURNED OFF SEATBELT SIGN. APU OFF; WE WAITED FOR EXTERNAL PWR AND JETWAY TO ARRIVE. OUR JUMP SEATER STOOD UP TO SAY GOOD-BYE AND UNLOCK COCKPIT DOOR. WHEN SHE DID; FLT ATTENDANT WAS THERE TO ASK US TO GET GATE INFO FOR HER NEXT FLT. WHILE FO DID THAT; I REACHED UP AND DID THE OVERHEAD PANEL PARKING FLOW; AND WITH NO EXTERNAL PWR; I PACKED MY CHARTS AND EAR PIECE. NEXT; I HAD A SHORT DISCUSSION ON THE USE OF ENG REVERSE ON LNDG WITH FO. HE THEN DID LOGBOOK. I WAS TURNED IN SEAT; AND STOOD UP TO LEAVE. FO WENT TO LAVATORY. I PICKED UP MY BAGS TO LEAVE. AT THAT TIME I BECAME AWARE OF ENG NOISE AND RETURNED TO MY SEAT AND SHUT DOWN L ENG. FO RETURNED AND WE DID PARKING CHKLIST. I BELIEVE A COMBINATION OF EVENTS CAUSED THIS: A TALKATIVE JUMP SEAT PAX; FLT ATTENDANT ASKING FOR INFO WERE DISTRACTING THE HABIT OF STARTING APU ON ARR AND SHUTTING DOWN BOTH ENGS IMMEDIATELY; AND A RESTLESS SHORT NIGHT LEFT US NOT AT OUR BEST LEVEL OF PERFORMANCE. FORTUNATELY; RAMP PERSONNEL FOLLOWED SOP AND DID NOT APCH THAT SIDE OF ACFT; AVERTING MORE SERIOUS CONSEQUENCES.