ACR Y HAD NMAC WITH ACR X VISUAL SEPARATION IN USE. ACR X TCASII RA. SEE AND AVOID CONCEPT.

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ACR X ON DEP FROM DEN; APPROX 15 DME N; 12000 FT ON ASSIGNED HDG OF 010 DEGS AND ASSIGNED TO CLB AT BEST ANGLE OF CLB -- 190-200 KTS IAS. DEP ADVISED US (128.05) OF TFC; ACR Y; AT OUR 6 O'CLOCK POS AND THAT THIS ACFT HAD VISUAL CONTACT WITH US. WE RECEIVED A SHORT TA ON TCASII (5 MI RANGE) SHOWING ACR Y AT 6 O'CLOCK AND 600 FT ABOVE SHORTLY FOLLOWED BY AN RA SHOWING ACR Y DIRECTLY OVERHEAD AT 400 FT. WHEN I ASKED THE CTLR TO VERIFY TFC; I WAS INFORMED THAT ACR Y STILL HAD VISUAL CONTACT WITH US. WE SHALLOWED OUR CLB PER TCASII INSTRUCTIONS. ACR Y WAS SPOTTED AT OUR 2-3 O'CLOCK POS AT ABOUT 400 FT AWAY AND THEN DIVERGING. AS A CREW; WE FELT ACR Y TO BE TOO CLOSE AND THAT ATC WAS LACKING IN KEEPING US INFORMED OF ACR Y POS. SUPPLEMENTAL INFO FROM ACN 251499: ACR X CLB VX (190 KTS) AND 010 DEG HDG AFTER TKOF. DEP THEN CLRED ACR Y TO CLB VFR BEHIND US AFTER SAYING HE HAD VISUAL CONTACT. DEP CTLR TOLD US OF THIS. BECAUSE OF OUR SPD DIFFERENCE WE RECEIVED A SHORT TCASII WARNING FROM BEHIND; BUT KNEW HE WOULD COME CLOSER THAN NORMAL AND THAT TCASII MIGHT GO OFF. WHEN IT WAS APPARENT THAT HE WASN'T JUST XING BEHIND US WE STARTED REDUCING OUR CLB. ACR Y CAME OVER TOP AT 400 FT ON TCASII WITH SLIGHT DIVERGENCE OFF R SIDE. WE FELT THAT DEP CTL DID NOT INSURE OUR SAFETY BUBBLE.