APCH CTLR STATED THAT CUSTOMS ACFT PENETRATED THE TCA WITHOUT CLRNC.

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AT APPROX XA05 HRS LCL TIME SMT DEPARTED RWY 29 AT NAS NORTH ISLAND; SAN DIEGO; CA; PROCEEDING SEBND ALONG THE COAST. AT XA08 HRS SMT CHKED IN WITH THE U.S. CUSTOMS RADAR FAC (C3I); WHOSE RADAR DISHES ARE LOCATED ATOP LAGUNA MOUNTAIN; 41 1/2 MI NE OF NZY. SMT TURNED EAST NORTH EAST BOUND AT XA11 ABEAM NAVY OUTLYING FIELD IMPERIAL BEACH. AS PIC SITTING THE LEFT SEAT; I WATCHED OLF IMPERIAL BEACH PASS BTWN MY SEAT AND THE LEFT NACELLE. ABOUT 4 MINS LATER I SAW BROWNFIELD ALSO PASS BELOW BTWN MY SEAT AND THE LEFT NACELLE. AT APPROX XA22 I TURNED N AND PROCEEDED DIRECTLY TO JULIAN VOR. I BEGAN MY TURN TO THE N AT 12800'. AFTER LNDG AND TALKING TO SAN TRACON; I CALLED AND SPOKE TO THE U.S. CUSTOMS RADAR OPERATOR WHO WAS GIVING ME FLT FOLLOWING. HE TOLD ME SMT WAS AT NO TIME MORE THAN 2 MI N OF THE MEXICAN BORDER AND WELL OUTSIDE THE SAN TCA. IN THE LAST 1 1/2 YRS SAN TRACON HAS TOLD ME I WAS IN MEXICAN AIRSPACE S OF THE U.S. BORDER WHEN IN FACT I WAS AT LEAST 1 MI N OF THE BORDER AND COULD SEE THE MEXICAN TOWN OF TECATE BELOW AND TO THE SO OF MY POS. TECATE IS A TOWN E OF BROWNFIELD AND BUILT RIGHT ON THE BORDER.