FLC OF A B757 FAILS TO RESPOND TO A TCASII RA. THEY IDENT ANOTHER ACFT BUT IT'S THE WRONG ONE FOR THE TCASII RA.

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ANOTHER 'HEADS UP' REGARDING TCASII. AT THE TCASII 'CAUTION' WE IDENTED 'ALERT' ACFT AS AN ACFT THAT WAS CLBING OUT OF LAX TOWARDS US. AT 'RED ALERT' WE RECONFIRMED ACFT CLBING AND DID NOT COMMENCE OUR CLRED DSCNT FROM 10000 FT TO 8000 FT. HOWEVER; WE DID NOT 'CLB' AS TCASII REQUESTED BECAUSE WE WERE IN VFR AND THOUGHT WE HAD VISUAL CONTACT. WE MISIDENTED THE TCASII ACFT AND THE OTHER; REAL TCASII ACFT WENT OFF OUR L WING DOING 250 KTS ABOUT 1 NM AWAY PASSING THROUGH OUR ALT! HE WAS UNDER DEP CTL; AND WE WERE ON APCH CTL. NEITHER ONE ADVISED THE OTHER. IN MY OPINION; ANY TIME TCASII ALERTS COME INTO PLAY LAX (SOCAL) NEEDS TO REEVALUATE THEIR DEP/ARR 'GAME PLANS.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS CONCERNED THAT ACFT CAME SO CLOSE TO HIM. THERE WAS ONLY 1 MI SEPARATION. HE DID RECEIVE A TCASII RA BUT INTERPRETED THE TCASII RA TO AN ACFT FLYING NEARBY. SINCE THEY HAD A VISUAL ON WHAT THEY THOUGHT WAS THE RA ACFT; THEY TOOK NO EVASIVE ACTION. SHORTLY THEREAFTER; THE TCASII RA ACFT CAME INTO VIEW AND STARTLED THE CAPT. BECAUSE THE ACFT CAME SO CLOSE; 6000 FT; HORIZLY; THE RPTR FEELS THAT ATC PROCS NEED TO BE REEVALUATED. CAPT NOW RESOLVES TO ALWAYS FOLLOW THE TCASII RA COMMANDS.