ARTCC RADAR CTLR ISSUED UNKNOWN TFC TO A DC9; THE DC9 FLC COULD NOT SEE THE TFC; HOWEVER; THEY RECEIVED A TCASII RA WHEN THE UNKNOWN TFC GOT CLOSER AND TOOK EVASIVE ACTION BY CLBING. THE CTLR ALSO ISSUED A TURN AWAY FROM THE OTHER ACFT.

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WHILE 4 ACFT WERE INBOUND TO PHL ON THE BUNTS1 ARR; I NOTICED A LIMITED DATA BLOCK 1200 CODE; CLBING OUT OF 7800 FT. I ISSUED TFC TO ACR X; THE FIRST ACFT; SAYING TFC WAS 1 O'CLOCK POS; 7 MI WBOUND; TYPE UNKNOWN; APPEARS TO BE CLBING OUT OF 7800 FT. THIS ACFT WAS ON A 1200 CODE; NOT BEING WORKED BY ANY CTLR. THE VFR ACFT CONTINUED TO CLB THROUGH 8000 AND 9000 FT AND HIGHER. I ISSUED TFC AGAIN TO ACR X. SINCE IT APPEARED TO BE A DEFINITE HEAD-ON SIT; I TOLD THE ACR X TO TURN L IF YOU DON'T HAVE TFC IN SIGHT. HE REPLIED WE DON'T HAVE HIM BUT HAVE HIM ON TCASII. WITHOUT THE L TURN; THEY WOULD HAVE POSSIBLY HIT OR BEEN VERY CLOSE TO IT. I THEN HAD TO TURN ANOTHER ACFT TO FOLLOW THE FIRST ONE AND ALSO AVOID THE VFR. THE VFR ACFT CAME CLOSE TO 3 ACFT; WITHOUT CALLING FOR ADVISORIES. I THEN GOT ACR X BACK ON COURSE AND NOW HAD TO ISSUE HOLD FOR 4 ACFT. AFTER IT WAS OVER; THE CAPT OF ACR X CALLED OUR AREA TO EXPRESS HIS GRATITUDE FOR MY TIMELY TA'S AND HIS CONCERN THAT THIS VFR ACFT COULD BE SO CLOSE WITHOUT BEING IN COM WITH ATC. HE STATED THAT WITHOUT THE TURN HE TOOK; IT COULD HAVE BEEN A COLLISION. HE WAS VERY CONCERNED ABOUT THIS VFR ACFT. I WAS TOO. THE VFR ACFT CALLED ON W OF LRP (ON THE WRONG FREQ) AND WAS TOLD BY THAT CTLR THAT ACFT HAD TO TAKE EVASIVE ACTION. HE WAS NOT TOO CONCERNED. SUPPLEMENTAL INFO FROM ACN 386359: WHILE EXECUTING THE BUNTS1 ARR TO PHL; AT 11000 FT JUST E OF LRP VOR; WE RECEIVED A TA FROM ZNY. THE RPTED TFC WAS IN OUR 1-2 O'CLOCK POS; 10 DME AND AT 8500 FT AND CLBING AND CLOSING (CONSTANT BEARING; DECREASING RANGE). I SEARCHED VISUALLY BUT UNABLE TO SEE THE CONFLICTING TFC. NEXT THE TCASII ISSUED A TA. AT THIS POINT THE CAPT ELECTED TO DEVIATE L (AWAY) FROM THE TFC. ATC THEN ISSUED THE SAME CLRNC JUST AS I WAS ABOUT TO XMIT OUR DEV INTENTIONS (ATC CLRED US TO DEVIATE AS NECESSARY TO THE L). NOW A TCASII RA WAS ISSUED. THE CAPT RESPONDED IMMEDIATELY TO THE RA; A CLB WAS MADE TO 12300 FT. THE TCASII RA AT THIS POINT CEASED. A CLRNC TO DSND AND VECTOR WAS THEN ISSUED BY ATC TO REJOIN THE ARR; NO FURTHER INCIDENTS OCCURRED. WE NEVER HAD THE OTHER ACFT VISUALLY. LATER ON WE WERE TOLD THAT THE OTHER ACFT (A SUPER KING AIR) HAD US VISUALLY. TCASII SAVED 55 LIVES THAT DAY ON OUR ACFT. FOR CORRECTIVE ACTION; THE OTHER ACFT SHOULD NEVER HAVE CLBED THROUGH OUR ALT; PERIOD. THERE WAS AN OBVIOUS MISJUDGMENT BY THE OTHER ACFT CREW ON SEPARATION OF ACFT. ANOTHER CONTRIBUTING FACTOR WAS THAT THE OTHER ACFT WAS OPERATING ON A DIFFERENT ATC FREQ. WX WAS NOT A FACTOR. THE ACTUAL CLOSEST POINT OF INTERCEPT; MAY HAVE BEEN A LOT LESS THAN 1.5 NM AND 400 FT. I SPENT MOST OF THE TIME OF THIS INCIDENT LOOKING OUTSIDE SO TO VISUALLY SEE THE TFC CONFLICT.