ACR X ON VISUAL APCH TO PARALLEL RWYS HAD NMAC. LTSS FROM ACR Z. SYS ERROR. EVASIVE ACTION TAKEN.

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AFTER RELIEVING AN FPL AND DEVELOPMENTAL OFF POS; I BEGAN TO ISSUE TFC TO ACR X TO SEE ACR Y ESTABLISHED ON THE RWY 25R ILS FINAL. AFTER ACR X RPTED ACR Y IN SIGHT I INSTRUCTED HIM TO FOLLOW AND CLRED VISUAL APCH RWY 25L. I TOLD ACR Y THAT TFC WOULD PULL UP ALONG HIS SIDE FOR RWY 25L. WITHIN 20 MI OF THE ARPT; ACR X STILL HAD NOT TURNED TO FOLLOW NOR DSNDED. I INSTRUCTED ACR X TO TURN R HDG 350 DEGS TO FOLLOW HIS TFC. WHILE I WAS WORKING OTHER ACFT; ACR X FLEW THROUGH FINAL INTO FLT PATH OF ACR Z HVY; WHO WAS DSNDING THROUGH 6000 ON THE RWY 24L ILS. I ISSUED A TA. ACR Z AND ACR X PASSED ABOVE HIM. AFTER THAT EPISODE; I WORKED TO RESEQUENCE ACR X. THERE WAS NO PROB OR INCIDENT AS FAR AS EVERYONE IS CONCERNED; BUT THIS TRULY SCARED ME; AND JUST IN CASE SOMEONE WANTS TO KNOW; I WANTED TO LET YOU GUYS KNOW. SUPPLEMENTAL INFO FROM ACN 247419: APCHING LAHAB INTXN; ONTARIO APCH SWITCHED US TO LAX APCH CTL WHO WAS OBVIOUSLY EXTREMELY BUSY. FINALLY; AFTER THE FOURTH ATTEMPT; THEY ANSWERED US AFTER I HAD ASKED IF THEY HAD ANY INSTRUCTIONS FOR US AFTER LAHAB. THEY SAID THAT WE SHOULD EXPECT TO FOLLOW A LARGE ACFT THAT WAS BEHIND US AND TO OUR R. IT WAS AT LEAST 8 MI BEHIND US. THE CTLR ASKED US IF WE HAD THE ACFT IN SIGHT; AND WE RESPONDED THAT WE DID HAVE THE ACFT IN SIGHT. THE CTLR SAID TO PULL UP BESIDE HIM BUT NOT TO PASS HIM. HE WOULD BE GOING TO 25R AND WE WERE CLRED FOR A VISUAL TO 25L. I TOLD THE CTLR THAT WE WOULD NOT BE ABLE TO STAY BEHIND HIM SINCE HE WAS STILL AT A CONSIDERABLE DISTANCE BEHIND US. AT THIS POINT A DIFFERENT CTLR CAME ON AND INSTRUCTED IS TO FLY HDG 360. WE WERE STILL AT 6000 FT MSL. WHEN WE WERE ESTABLISHED ON THIS HDG; THE PF IN THE R SEAT CALLED CONFLICTING TFC INBOUND TO LAX AT 2 O'CLOCK; SLIGHTLY BELOW US. WE IMMEDIATELY CLBED TO AVOID COLLIDING WITH THE OTHER ACFT. WE WERE SUBSEQUENTLY VECTORED AND RESEQUENCED BEHIND AN MLG.