INSTRUCTOR PLT IN AN MO20 ON SHORT FINAL FOR RWY 29R SAW AN UNKNOWN ACFT PASS OVER THE TOP OF HIM AND LAND. THE MO20 TOOK EVASIVE ACTION TO MISS THE UNKNOWN ACFT AND DID NOT HEAR ANY RADIO COM BTWN THE TWR AND THE UNKNOWN ACFT. ATCT LCL CTLR SEEMED SURPRISED AT THE POS OF THE UNKNOWN ACFT AND LATER DID NOT WANT TO DISCUSS THE SIT WITH THE RPTR.

Narrative

WE WERE PERFORMING FULL STOP NIGHT TKOF AND LNDGS ON RWY 29L. WE HAD REQUESTED A THIRD AND FINAL LNDG BEFORE RETURNING TO THE HANGAR. OUR TKOF WAS ON RWY 29L AND WHILE ON DOWNWIND WE WERE CLRED TO LAND ON RWY 29R. ON L BASE TO RWY 29R; WE NOTICED ANOTHER ACFT TO THE N AND E OF US THAT APPEARED TO BE COMING S (FROM OVER HWY 36) AND ON A PATH SIMILAR TO A WIDE R BASE FOR RWY 29R. THE ACFT WAS ESTIMATED TO BE APPROX 500 FT ABOVE US AND WAS THOUGHT TO BE OVERFLYING THE AREA; AS WE HAD NOT HEARD ANY RADIO COMS BTWN THE TWR AND ANY ACFT RELATIVE TO LNDG WHILE WE WERE IN THE PATTERN FOR THIS LNDG. AFTER WE HAD TURNED FINAL; WE ATTEMPTED TO KEEP THIS ACFT IN VIEW. FROM THE COPLT'S POS; I OBSERVED THAT THE ACFT HAD ALSO TURNED TO A COURSE PARALLELING THE RWY AND WAS CATCHING UP TO US. WHEN THE ACFT WAS DIRECTLY ABOVE US; AND JUST BARELY VISIBLE AT THE TOP OF OUR WINDSCREEN IT WAS OBSERVED TO TURN ON ITS LNDG LIGHT. AT THAT POINT WE WERE ON APPROX A 1/2 MI FINAL AND APPROX 200 FT AGL. THE GAP BTWN US RAPIDLY CLOSED TO APPROX 200 VERT FT. OUR EVASIVE ACTION WAS TO TURN TO A MORE NW HDG. WE THEN PARALLELED RWY 29R ON THE N SIDE. WE WERE LATER CLRED BY THE TWR TO MAKE L TFC AND WE MADE AN UNEVENTFUL LNDG ON RWY 29R. THE TWR NOTICED BOTH ACFT WERE ON FINAL FOR RWY 29R AFTER THE OTHER ACFT HAD TURNED ON ITS LNDG LIGHT. THEIR COMMENT ABOUT THIS OBSERVATION INDICATED TO US THAT THEY WERE JUST AS SURPRISED AS WE WERE. THE OTHER ACFT DID NOT ACKNOWLEDGE THE TWR'S CALL; BUT WHEN WE WERE WELL CLR WE NOTIFIED THE TWR THAT WE HAD DEVIATED TO THE NW AS OUR EVASIVE ACTION. WHILE WE WERE CONDUCTING OUR THIRD LNDG; WE DID NOT AT ANY TIME HEAR ANY COMS BTWN THE TWR AND ANY OTHER ACFT RELATIVE TO 'PERMISSION TO LAND.' AT APPROX XA45 LCL; THE PLT CONTACTED THE JEFFCO CTL TWR BY TELEPHONE. HE ATTEMPTED TO DISCUSS THE SIT WITH THEM. THE TWR PERSONNEL CHOSE NOT TO PROVIDE HIM WITH ANY SIGNIFICANT DETAILS AT THAT TIME.