BROCKWAY AIR FLT 993 (BE-1900C, N7254R) WAS CLRD TO LND ON RWY 28 AS ICARUS 60 (MITSUBISHI MU-2B, N638MA) WAS TAXIING TO RWY 28, VIA THE PARALLEL TWY (ALPHA). WX WAS IN PART: PTLY OBSCD, 200' OVC, VIS 3/4 MI WITH LGT DRZL & FOG, WND CALM. WHILE LNDG, FLT 993 WAS ADZD TO TURN RGT WHEN ABLE & TO CTC GND CTL 'LEAVING THE RUNWAY.' AT 1216:53 EST, FLT 993 TMTD TO GND CTL THAT THE FLT WAS OFF THE RWY. AT 1217:00, GND CTLR TOLD FLT 993 TO 'GIVE WAY TO THE MITSUBISHI, THEN TAXI TO RAMP VIA ECHO. . .' AT ABT THAT TIME, AN ELT ACTVTD AS THE 2 ACFT COLLIDED. INV REVEALED 1ST OFFICER OF FLT 993 MADE THE LNDG, TURNED OFF ON TWY ECHO & BGN TO CROSS TWY ALPHA. TWY ECHO ANGLED OFF THE RWY, BUT WAS NOT A HIGH SPEED TWY, THO CAPT OF FLT 993 THOUGHT IT WAS. COLLISION OCCURRED AT INTXN OF TWYS. NEITHER CREW SAW THE OTR ACFT UNTIL MOMENTS BFR IMPACT. CTLR'S VIEW OF TWY ALPHA WAS PARTLY BLOCKED BY OBSTNS; GND CTLR DID NOT ADZ ICARUS 60 OF PSN OF FLT 993 OR INSTRUCT HIM TO HOLD SHORT OF INTXN. CAPT OF ICARUS 60 HAD LOOKED AWAY FOR ANOTHER ACFT JUST BFR IMPACT.