POSSIBLE NMAC OCCURRED WHEN A DEPARTING ACR B727 DRIFTED OFF COURSE WHILE SEARCHING FOR A VFR CESSNA DISPLAYED ON TCASII. FLC RECEIVED AN RA TO CLB. FLC QUERIED THE TWR ABOUT THE TFC AND WERE TOLD IT WAS 1 MI TO THE W OF THE LOC AND THAT THEY WERE L OF THE LOC AND TO CORRECT BACK. OTHER TFC AT 10-11 O'CLOCK INBOUND OBSERVED ON TCASII AND VISUALLY.

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I WAS FLYING THE ACFT AS FO. WHEN CLRED FOR TKOF; I OBSERVED A LIGHT ACFT (PROBABLY A CESSNA -- IT HAD A HIGH WING) DEPARTING AHEAD OF US; TURNING SSW; AWAY FROM THE DEP COURSE. NO ADVISORY CONCERNING THAT TFC WAS GIVEN TO US BY TWR WHEN TKOF CLRNC WAS ISSUED. WHEN INITIATING THE TKOF; I EXPECTED THAT THE LIGHT ACFT WOULD CONTINUE TO DIVERGE FROM OUR DEP COURSE. AFTER TKOF AND DURING INITIAL CLBOUT; I WAS UNABLE TO ACQUIRE THE TFC VISUALLY; SO I MADE A POINT OF CHKING THE TCASII DISPLAY; WHICH SHOWED TFC DIRECTLY AHEAD ABOUT 700 FT ABOVE US; AT ABOUT 2 NM. (FIRST RANGE MARK ON 5 NM SCOPE.) AT THAT TIME; I INITIATED A RADIO CALL TO TWR 'WHERE'S THE TFC FOR ACR X?' THE REPLY WAS EITHER UNREADABLE OR 'STEPPED ON;' BUT I THINK HE SAID 'CALLING TWR; SAY AGAIN.' THE CAPT THEN ADVISED TWR OF OUR TCASII TFC AT 12 O'CLOCK; THE REPLY WAS THAT THE TFC WAS 1 NM W OF THE LOC AND DIVERGING W. BUT OUR DISPLAY BY THEN SHOWED IT NEARLY ON TOP OF OUR OWN ACFT TCASII SYMBOL. ABOUT THE SAME TIME WE RECEIVED AN RA (TCASII RA) TO CONTINUE CLB AT GREATER THAN 2000 FPM. OUR CLB WAS ALREADY MAXED OUT AT ABOUT 2200-2500 FPM. OUR ATTN WAS PRIMARILY FOCUSED OUTSIDE; SEARCHING OUR FORWARD SECTOR VISUALLY FOR THE TFC WHICH WE NEVER DID VISUALLY ACQUIRE. (ACCORDING TO OUR TCASII WE PASSED DIRECTLY OVERHEAD THE TFC.) DURING THIS TIME OUR DEP FLT PATH HAD DRIFTED TO THE L OF THE LOC. TWR ADVISED US TO CORRECT BACK R; WHICH I AGGRESSIVELY DID. TWR ALSO ADVISED US OF ADDITIONAL TFC AT APPROX 10 O'CLOCK; WHICH WE ALSO HAD ON TCASII AND VISUALLY; AND WAS NO FACTOR. I BELIEVE OUR DEV E OF THE DEP COURSE WAS CAUSED BY TCASII ADVISORY REQUIRING GREATER OUTSIDE VIGILANCE AND TWR DENYING THE CONFLICT.