WHILE TAXIING TO THE GATE AFTER LNDG AT OKC; FLT CREW OF B757-200 ARE SHOCKED TO SEE ACFT PASS DIRECTLY OVER THEM; MISSING A COLLISION BY A NARROW MARGIN.

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RWY 35R WAS USED FOR LNDG. TURNOFF FROM THE RWY WAS EXECUTED AT TXWY E2 OR TXWY E FOLLOWED BY A SBOUND TAXI ON TXWY E. WE ADVISED THE TWR OF OUR GATE AND THE TWR RESPONDED THAT WE WERE TO REMAIN ON HIS FREQ AND TAXI TO THE GATE. A SPECIFIC RTE WAS SPECIFIED TO THE GATE. INITIAL TAXI WAS UNEVENTFUL. THERE WERE SEVERAL ACFT ON THE TWR FREQ. JUST PRIOR TO TURNING R FROM TXWY E TO TXWY G; BOTH PLTS LOOKED BOTH WAYS FOR CONFLICTING GND TFC. AS I LOOKED L; I NOTICED SOME LIGHTS IN THE SKY; POINTED IN OUR DIRECTION; AT SOME UNDERMINED DISTANCE. THE LIGHTS WERE CLRLY LNDG LIGHTS AND THE ACFT WAS POINTED AT US; BUT THE DISTANCE COULD HAVE BEEN UP TO 10 MI. THE LIGHTS WERE NOT PERCEPTIBLY MOVING. WE MADE THE TURN FROM TXWY E TO TXWY G. AS WE PASSED TXWY K; I LOOKED UP FROM THE TAXI CHART TO SEE THE WHITE TAIL LIGHTS OF AN ACFT IN FRONT OF US; ALOFT; BUT VERY CLOSE TO THE GND. SIMULTANEOUSLY; THE CAPT SAID 'OH MY GOD.' IT WAS IMMEDIATELY CLR TO BOTH OF US THAT WE HAD BEEN OVERFLOWN AT AN EXTREMELY LOW ALT BY ANOTHER ACFT. THE OVERFLYING ACFT APPEARED TO BE ABOUT 50-100 FT AGL; AND DID NOT CLB. 2-4 SECONDS LATER; THE CTLR; IN A RELAXED VOICE; SAID 'TWIN COMMANDER; YOU DO NOT APPEAR TO BE LINED UP WITH THE RWY; GO AROUND.' THE LOW FLYING ACFT; NOW IDENTED AS TWIN COMMANDER; MADE NO IMMEDIATE EFFORT TO CLB; AND IN FACT FROM MY VANTAGE POINT; THE TWIN COMMANDER APPEARED TO DSND SLIGHTLY. I BELIEVED THAT THE TWIN COMMANDER WAS HEADED FOR THE GND AND WOULD CRASH. WE MOMENTARILY STOPPED OUR TAXI; THEN CONTINUED WITHOUT INCIDENT. A NUMBER OF SECONDS LATER; THE TWIN COMMANDER STARTED A SLOW CLB. ABOUT 10 SECONDS AFTER THE TWIN COMMANDER EXECUTED THE GAR; THE TWR TOLD THE TWIN COMMANDER TO 'TURN L FOR A L DOWNWIND FOR RWY 35L. I WILL PUT YOU IN FRONT OF ANOTHER ACFT.' THE TWIN COMMANDER DID NOT TURN BUT CONTINUED STRAIGHT W. SUPPLEMENTAL INFO FROM ACN 658606: I CONTACTED THE TWR AFTER LNDG TO REQUEST THAT THEY FILE AN NMAC RPT.