AN ACR IS CLRED TO CROSS RWY 9L AT PHL; PA. ANOTHER ACR ON TKOF ROLL ON THAT RWY QUESTIONS THE LCL CTLR ABOUT THE CONFLICT ONCE HE IS AIRBORNE.

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TAXI INSTRUCTIONS IN PHL WERE TO TAXI S ON TXWY E; HOLD SHORT OF RWY 9L. WE COMPLIED AND THEN WERE CLRED TO CROSS RWY 9L ON TXWY E. I SWITCHED ON OUR STROBES AND WING ICE LIGHTS AND PROCEEDED TO CROSS. WE COULD SEE AN ACFT ON THE DEP END OF RWY 9L BUT NO MOVEMENT WAS VISIBLE. AS WE ENTERED THE RWY; WE WERE INSTRUCTED BY GND CTL TO TAXI ACROSS RWY 9L WITHOUT DELAY DUE TO TFC DEPARTING RWY 9L. AS WE EXITED THE OTHER SIDE OF RWY 9L ON TXWY E; WE COULD SEE A NARROW BODY; TWIN JET APCHING FROM OUR R; LIGHTS ON; TAKING OFF FROM RWY 9L. AS WE SWITCHED TO TWR FREQ WE HEARD THAT SAME DEPARTING FLT QUERY THE TWR CTLR; 'ARE YOU AWARE AN ACFT CROSSED THE RWY IN FRONT OF US ON THE TKOF ROLL?' THE TWR CTLR REPLIED 'YES' AFTER A LONG PAUSE. HAD WE SEEN THAT THE FLT WAS MOVING ON THE RWY FOR TKOF WITH LIGHTS ON; WE WOULD NOT HAVE PROCEEDED ACROSS RWY 9L AND WOULD HAVE HELD SHORT. AS WE CLRED THE RWY; THE DEPARTING FLT WAS LIKELY BTWN TXWY T AND TXWY K4 ON THE TKOF ROLL. IT SHOULD NOT HAVE BEEN CLRED FOR TKOF BEFORE WE ENTERED THE RWY WHICH IS WHAT PROBABLY HAPPENED. I WILL CONTINUE TO BE VIGILANT IN CHKING FOR LNDG/DEPARTING TFC AS WELL AS XING/HOLD SHORT CLRNCS BEFORE XING ANY RWY. SUPPLEMENTAL INFO FROM ACN 556334: ACFT CLRED FOR TKOF; QUESTIONED WHETHER OR NOT I KNEW THAT ANOTHER ACFT HAD CROSSED THE RWY AHEAD OF HIM. SUPPLEMENTAL INFO FROM ACN 556335: I VERBALLY REQUESTED APPROVAL TO CROSS RWY 9L AT TXWY E WITH ACFT X. THE LCL E CTLR VERBALLY APPROVED MY REQUEST AND I ISSUED INSTRUCTIONS TO ACFT X TO CROSS RWY 9L AT TXWY E. AT NO TIME DID THE AMASS ALARM ISSUE ANY WARNINGS.