SMA ON VISUAL APCH HAD WRONG ACFT IN SIGHT AND SMT TOOK EVASIVE ACTION TO MISS SMA.

Narrative

LTT X WAS BEING VECTORED FOR A VISUAL APCH TO RWY 21R. SMA Y WAS BEING VECTORED TO FOLLOW LTT X. THERE WAS ALSO AN LGT BEING VECTORED FOR THE PARALLEL RWY 21L. LTT X CALLED W LCL CTL 8 MI FINAL; AND WAS CLRD TO LAND RWY 21R. SMA Y WAS ON A PARALLEL COURSE TO LTT X'S RIGHT. SMA Y CALLED TWR AND WAS AGAIN INSTRUCTED #2 FOLLOWING LTT X TFC. SMA Y ADVISED TWR HE HAD HIM IN SIGHT. SMA Y APPEARED TO BE OVERTAKING LTT X. SMA Y WAS ASKED IF HE STILL HAD HIS TFC TO FOLLOW IN SIGHT. HE REPLIED WITH A NEGATIVE STATEMENT; AND THAT HE THOUGHT HE MIGHT BE FOLLOWING THE WRONG ACFT (THE LGT ON FINAL FOR RWY 21C). SMA Y WAS ISSUED AN IMMEDIATE RIGHT TURN HDG 270 DEGS. THE TARGETS WERE MERGING ON RADAR. SMA X; FROM THE EYES OF THE TWR; APPEARED TO BE IN FRONT OF LTT X AND TURNING W. LTT X STARTED A CLB TO AVOID TFC. LTT X ELECTED TO CONTINUE THE APCH AND LAND RWY 21R. SMA Y WAS GIVEN A RIGHT 360 DEG TURN TO FINAL AND LANDED RWY 21R W/O FURTHER INCIDENCE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR GAVE EXPERIENCE LEVEL. NO SPECIFIC DISTANCE WAS MENTIONED ON NMAC; BUT TARGETS DID MERGE ON THE BRITE RADAR. TFC HAD BEEN GIVEN TO BOTH ACFT AND SMA HAD STATED THE SMT WAS IN SIGHT. RPTR FEELS THAT SMA HAD ANOTHER ACFT AND NOT THE SMT IN SIGHT. SMT DIDN'T SEE THE SMA UNTIL HE STARTED A TURN TO THE W; AND AT THAT TIME; SMT PULLED UP TO MISS THE SMA. LOCATION OF INCIDENT WAS ON FINAL APCH RWY 21R; APPROX 5 MI.