AN ACR MLG ON A VISUAL APCH AT NIGHT TO RWY 25R AT LAS WAS GIVEN A GAR WHILE ON SHORT FINAL DUE TO A B737 IN POS AND HOLD AT THE END OF THE RWY. TWR CTLR HAD BEEN MOMENTARILY DISTRACTED BY HELI TFC THAT HAD DELAYED THE B737 TKOF CLRNC. THE MLG FLC CITES B737 NOT HAVING STROBE LIGHTS ON TO MAKE HIM MORE VISIBLE WHILE IN THE OVERRUN.

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WE WERE CLRED FOR A VISUAL APCH TO RWY 25R AT LAS AND TO FOLLOW ANOTHER ACFT ON RWY 25L. KEEPING VISUAL CONTACT ON PRECEDING ACFT WAS DIFFICULT DUE TO GND LIGHTS. WE OBSERVED ACFT TURN OFF HIS RWY AND CROSS OURS (RWY 25R). WITHIN APPROX 30 SECONDS; APPROX 150-200 FT AGL; WE WERE DIRECTED BY TWR TO 'GAR.' A NORMAL GAR WAS FLOWN AND VISUAL PATTERN BACK TO VISUAL LNDG. AS THE GAR WAS INITIATED; THE CAPT (NON-FLYING) LOOKED DOWN AND SAW A B737 SITTING IN THE DISPLACED THRESHOLD OF RWY 25R. WE DID NOT SEE THE ACFT UNTIL TOLD BY TWR TO GAR. ACFT ON RWY DID NOT HAVE STROBES ON NOR WERE ANY OTHER LIGHTS OBSERVED BY US. AFTER LNDG; TWR CTLR WAS CONTACTED. HE STATED THAT AFTER THE B737 WAS CLRED ONTO RWY 25R; HE WAS DISTRACTED BY HELI TFC THAT DELAYED THE TKOF OF THE B737 ON RWY. OUR LACK OF ANY VISUAL CLUES TO THE PRESENCE OF THE B737 ON THE RWY AND THE DISTR OF THE TWR CTLR; COULD HAVE LED TO A 'POTENTIAL CONFLICT.' WE COULD NOT SEE ACFT UNTIL ILLUMINATED BY OUR LNDG LIGHTS AND AFTER DIRECTED BY TWR TO GAR. SUPPLEMENTAL INFO FROM ACN 386139: RWY 25R HAS AN APPROX 1000 FT DISPLACED THRESHOLD THAT IS LIGHTED WITH WHITE LIGHTS IN AN UPSIDE DOWN 'T' ARRANGEMENT; AND IS THE NORMAL TKOF POS UTILIZED DAY OR NIGHT. THIS ATTRIBUTED TO A GREATER THAN NORMAL SEPARATION BUT ALSO MASKED THE ACFT IN THE OVERRUN LIGHTS. WE HAD BEEN CLRED TO LAND NEARLY 7 NM OUT ON FINAL AND WERE SOMEWHAT CONCERNED ABOUT A PARALLEL VISUAL ACFT TO RWY 25L UNTIL WE SAW HIM LAND AND CLR OUR RWY. AT NO TIME WERE TOLD THE ACR ACFT WAS HOLDING ON OUR RWY. I BELIEVE THE FARS SHOULD MAKE IT MANDATORY STROBE LIGHT BE USED WHEN TAKING THE RWY RATHER THAN JUST VOLUNTARY.