Emad Salem was the FBI's informant. I typed 'World Trade Center bombing informant 1993' into www.google.com and got the name of the guy, then did a search for 'Emad A Salem' and got some more stuff. Too much to sift through right now, but here's something that jumps out, from a New York Times piece:

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The transcript quotes Mr. Salem as saying that he wanted to complain to F.B.I. headquarters in Washington about the bureau's failure to stop the bombing, but was dissuaded by an agent he identified as John Anticev.

"He said, I don't think the New York people would like the things out of the New York office to go to Washington, D.C.," Mr. Salem said Mr. Anticev told him.

[SNIP]

In another point in the transcripts, Mr. Salem recounts a conversation he said he had with Mr. Anticev, saying ,"I said 'Guys, now you both saw this bomb went off and you both know that we could avoid that.'" At another point, Mr. Salem says, "You get paid, guys, to prevent problems like this from happening."

Mr. Salem talks of the plan to substitute harmless powder for explosives during another conversation with agent Floyd. In that conversation he recalls a previous discussion with Mr. Anticev.

"Do you deny," Mr. Salem says he told the agent, "your supervisor is the main reason of bombing the World Trade Center?" Mr. Salem said Mr. Anticev did not deny it. "We was handling the case perfectly well until the supervisor messed it up, upside down."

http://users.crocker.com/~acacia/text_wtc_fbi.html
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I'll look for the quote where Salem says he was ordered to 'let the bombing go forward'. Thousands of URLS...it's there somewhere. The FBI blew up the bomb in 1993.

You might want to do some searches on Salem, etc.