LESS THAN STANDARD SEPARATION BETWEEN 2 ACR ACFT ON APCH TO LAX.

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WHILE BEING VECTORED TO EXPECT A RWY 25R LNDG; HDG 330 DEGS; LAX APCH CALLED TFC TO FOLLOW; ACR ABC FLT Z ON A RWY 25L APCH AT OUR 11 O'CLOCK POS. TFC AT 11 O'CLOCK WAS VISIBLE; IDENT AS COMPANY ABC WAS NOT POSSIBLE WITH THE HAZE AND VIS PRESENT. ATC INFORMED US TO FOLLOW THIS TFC FOR A VISUAL APCH TO RWY 25R. WE TURNED TO AN INTERCEPT HDG TO FOLLOW ACR Z; RWY NOT IN SIGHT; SPACING NOW ESTIMATED 4-5 MI BEHIND ACFT WE EXPECTED TO FOLLOW. THEN LGT Y; SAME COMPANY AS Z; APPEARED AT 11 O'CLOCK; 1/2-1 MI; AND 500' BELOW. CAPT IMMEDIATELY INFORMED APCH OF THE CONFLICT OF TFC. APCH CTLR INFORMED US; 'IT APPEARS TO BE NO PROB; CONTINUE.' AS WE CONTINUED TO SLOW TO APCH SPD TO FOLLOW THE CURRENTLY SPOTTED LGT Y; WE AGAIN QUERIED THE CTLR TO INSURE THE TFC WE NOW ARE FOLLOWING IS THE CORRECT TFC AND THAT WE MAY HAVE ATTEMPTED TO FOLLOW THE IMPROPER TFC ORIGINALLY. THE RWY DID NOT BECOME VISIBLE UNTIL APPROX 3 MI FROM THE RWY. AT THIS TIME A SIDESTEP TO RWY 25R WAS ACCOMPLISHED W/O FURTHER CONFLICT. CONTRIBUTING FACTORS AND HUMAN CONSIDERATIONS TO CONSIDER MAY INCLUDE THE FOLLOWING: 1) TFC CALLED AT 11 O'CLOCK ON APCH TO RWY 25L COULD NOT POSITIVELY BE IDENTED AS ABC AIRLINE; BUT ONLY 1 ACFT WAS CURRENTLY AT OUR 11 O'CLOCK POS AT THIS TIME AND IN POS FOR A RWY 25L APCH. 2) LIMITED VIS; MARGINAL FOR VISUAL APCH. 3) BOTH CAPT AND F/O ON LAST LEG OF AN 8 HR HARD TIME FLYING DAY; E TO W COAST TRIP; 12 HR DUTY DAY. 4) LOC FOR RWY 25R OTS; AS PER ATIS. 5) FLT CREW WAS E BASED; PREVIOUS OPERATION AND FAMILIARITY WITH LAX APPROX 6 PREVIOUS OPS INTO LAX. I BELIEVE THAT HAD THE APCH CTLR POINTED OUT THE INITIAL TFC THAT WE IDENTED AS OUR ONLY 11 O'CLOCK TFC VISIBLE; IN ADDITION TO POINTING OUT ADDITIONAL TFC ON THAT APCH; IE; LGT ACR Y WHICH MUST HAVE BEEN AT OUR 1-2 O'CLOCK POS AT THE TIME OF CALL OUT; THIS CONFLICT COULD HAVE EASILY BEEN AVERTED. AS PREVIOUSLY MENTIONED; THE SECOND LGT Y WAS NOT OBSERVED ON THE APCH PRIOR TO OUR SIGHTING AT 1/2-1 MI AND 500' BELOW. THE LIMITED VIS WAS A DEFINITE FACTOR IN PROPER RECOGNITION AND OBSERVANCE OF THE TFC FOR A VISUAL APCH. SUPPLEMENTAL INFO FROM ACN 90540: TUNED IN LOC FOR RWY 25R AND USED IT FOR GUIDANCE TO RWY 25R (ATIS BROADCAST ILS 25R O/S) LOC SIGNAL LINED US UP FOR RWY 25L. PICKED UP RWY 25R VISUALLY AT 3 DME AND LANDED ON RWY 25R. CONTRIBUTING FACTORS: 1) CTLR--UNCERTAIN OF TFC POS. 2) FLT CREW--UNAWARE OF CONFLICTING TFC. THIS WAS THE LAST LEG OF 5; TOTAL FLYING TIME 7:59 HRS. IT SEEMS THAT THERE IS OFTEN SUBTLE PRESSURE PUT ON THE FLT CREW BY CTLRS AT HIGH VOL ARPTS TO BE 'SUCKED IN' TO THAT VISUAL APCH WHEN VISUAL CONDITIONS ARE LESS THAN OPTIMUM.