A B767-300 FO RPTED THAT THE CAPT CROSSED THE HOLD SHORT LINE FOR RWY 25R WITHOUT PERMISSION AT LAX.

Narrative

AFTER LNDG ON RWY 25L AT LAX; WE WERE TOLD TO HOLD SHORT OF RWY 25R WHILE ON THE ROLLOUT DUE TO DEPARTING TFC. AS WE TURNED OFF AT TXWY P; I WAS BEGINNING THE AFTER LNDG FLOW AND WHEN I LOOKED UP; IT APPEARED THAT THE CAPT WAS GOING TO CROSS RWY 25R. I SAID 'STOP;' BUT WAS TOO LATE. IT APPEARED THAT WE HAD CROSSED THE HOLD SHORT LINE; BUT WAS DIFFICULT TO TELL HOW FAR. A B747-400 WAS ON THE TKOF ROLL AND WAS NOT TOLD TO ABORT. THE B747 ROLLED BEYOND OUR TXWY BEFORE IT WAS AIRBORNE AND HAD PLENTY OF CLRNC. ALSO; TWR DID NOT SAY ANYTHING TO US ABOUT XING THE HOLD SHORT LINE. THE WX AT LAX WAS LOW VISIBILITY AND RAINING AT THE TIME THIS OCCURRED. ALSO; WE WERE IN A NEW B767-300 THAT HAS SOME DIFFERENCES FROM THE REST OF THE B767 FLEET. THIS WAS MY FIRST TIME EVER TO SEE THIS AIRPLANE; WHICH CAUSED MY AFTER LNDG FLOW TO TAKE LONGER THAN NORMAL. IF I WASN'T DISTR BY THIS NEW AIRPLANE; I WOULD HAVE NOTICED THE CAPT WAS NOT GOING TO STOP SOONER AND COULD HAVE PREVENTED US FROM XING THE HOLD SHORT LINE.