ACR ACFT RECEIVED RA WHILE ON FINAL TO LAX. TFC HAD BEEN ISSUED ON PARALLEL BUT CTLR FAILED TO ADVISE PLT OF HELI OPERATING BELOW THE APCH.

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WE WERE CLRED FOR THE RWY 25L ILS APCH OUTSIDE OF HUNDA INTXN. WE WERE TOLD ABOUT TFC AT 10 O'CLOCK POS AND ABOUT 2 MI; A B757. WE RPTED TFC IN SIGHT. WE WERE TOLD TO MAINTAIN 180 KTS TO THE MARKER. AS THE CAPT INTERCEPTED THE GS AND STARTED THE DSCNT; WE RECEIVED A TA FROM TCASII. IN THE NEXT FEW SECONDS A LOT OF THINGS WERE HAPPENING VERY FAST. I FIRST THOUGHT THE TA WAS FROM THE B757 AT OUR 1 O'CLOCK POS GOING TO RWY 24R. I HAD HIM IN SIGHT AND KNEW HE WASN'T A PROB. THEN WE RECEIVED OUR FIRST RA WHICH WAS TO DSND; FOLLOWED BY AN RA TO CLB AND THEN AN RA TO 'MONITOR VERT SPD.' DURING THIS PROCESS I LOOKED AT THE TCASII AND NOTED TFC DIRECTLY UNDER AND 200 FT BELOW US. WE NEVER SAW ANYTHING. THE CAPT FOLLOWED THE RA TO CLB AND CLBED FROM ABOUT 2800-3100 FT MSL BEFORE RA ENDED. I ASKED LAX TWR IF THEY HAD TFC AT OUR POS. THEY SAID; 'YES WE HAVE HELI TFC BELOW YOU.' ATC SHOULD HAVE POINTED OUT TFC BEFORE WE APCHED THEIR POS AND TFC SHOULD NOT BE ALLOWED THAT CLOSE TO SUCH A BUSY INST APCH.