From the pictures I saw of the market, plus the eyewitness accounts, it didn't look like it could possibly have been caused by a Tomahawk or a bomb, as the media were speculating. It seemed to have been a relatively small blast with a lot of fragmentation. My initial suspicion was Iraqi artillery - not AAA, but a deliberate artillery attack to pin the blame on the US. But Fisk's find has given me reason to revisit this. I now believe the cause was probably a US High Speed Anti-Radiation Missile (HARM) fired from a USAF F-16. How do I know? Thanks to reporting from the blast site, with a lot of help from Mr Google. Let me run you through it briefly.

The serial number found by Fisk is almost identical to the serial number of a LAU- 118 underwing missile launcher, as described here.

This is the important bit. Note the P/N and CAGE numbers, which when put together look eerily similar to Fisk's number (30003-704ASB 7492):