2 GA ACFT AT PRC HAVE NMAC DURING PATTERN ENTRY.

Narrative

I WAS WORKING THE LCL CTL 2 POS; CTLING ACFT USING RWY 21R AND IN AND OUT OF CLASS D AIRSPACE FROM THE W. ACFT X WAS DOING PATTERN OPS ON RWY 21R. THEY REQUESTED A FULL STOP LNDG. SINCE ACFT X PARKS SE OF RWY 21L; I HANDED THE ACFT X OFF TO THE LCL-1 CTLR. APPROX 2 MI SW OF THE ARPT IS A HOUSE WHOSE RESIDENT COMPLAINTS WHEN ACFT OVERFLY HER HOUSE. TO AVOID THE HOUSE; ACFT Y FLEW A WIDE PATTERN. I WAS LISTENING AS THE LCL-1 CTLR WAS TALKING TO THE 2 ACFT. WHEN THE LCL-1 CTLR TOLD ACFT Y TO ENTER A WIDE DOWNWIND; I LOOKED TOWARDS ACFT X. I THEN OBSERVED ACFT Y PASS IN FRONT OF ACFT X. THEY WERE SO CLOSE I THOUGHT THEY WERE GOING TO HIT. AFTER THEY PASSED; I POINTED OUT ACFT Y TO THE LCL-1 CTLR. ACFT Y WAS RPTING A STANDARD PATTERN ENTRY; AND THE ACFT IS BASED HERE. THE ONLY WAY ANY OF US IN THE TWR COULD HAVE HELPED ACFT X IS WITH A TWR RADAR DISPLAY. SUPPLEMENTAL INFO FROM ACN 469744: ONE ACFT WAS ENTERING PATTERN WHILE THE OTHER ACFT WAS CHANGING FROM ONE RWY TO THE OTHER FROM THE PATTERN ALT PRIOR TO LNDG ON PARALLEL RWY. THE NEAR MISS OCCURRED AS ONE ACFT WAS TURNING FROM XWIND TO DOWNWIND WHILE THE OTHER ACFT WAS ABOUT TO TURN FROM THE 45 DEG ENTRY TO L DOWNWIND. CONTRIBUTING FACTORS WERE PLTS NOT EXPECTING TFC AT THE POINT OF CONTACT AND THE USE OF 2 RADIO FREQS JUST PRIOR TO INCIDENT. CALLBACK CONVERSATION WITH RPTR ACN 469483 REVEALED THE FOLLOWING INFO: RPTR SAID HE DID NOT KNOW THE OUTCOME OF THE NMAC. HE BELIEVED IT WAS STILL UNDER INVESTIGATION BY THE FSDO. HE DID NOT ADD ANY ADDITIONAL INFO.