IF IT WAS A BOMB, THEN WHODUNIT?

The ocean stubbornly held on to its mysteries for most of last week. It was especially uncooperative on Thursday for the men and women investigating the crash of TWA Flight 800. Rain and strong winds disrupted and eventually interrupted search operations. But on Friday there was a breakthrough. Deep Drone 7200, a remotely operated robot outfitted with cameras that can explore ocean depths without divers, located part of the cockpit, "the nerve center of the aircraft," as Robert Francis, vice chairman of the National Transportation Safety Board (NTSB), described it. Said James Kallstrom, the FBI's lead investigator: "I just think that somewhere in the front of the plane is a clue." Investigators generally believe that if a bomb destroyed Flight 800, it exploded in the front of the aircraft. Examining the cockpit could help prove that theory.

As the Navy continued to search for and recover bodies, investigators have begun to speculate not only about the cause of the disaster but also about the originators of what they are almost certain is a monstrous crime. A well-placed U.S. intelligence source has told TIME that calls and transmissions tracked by the CIA out of Tehran "have raised suspicions" that there is an Iranian connection to the crash. The CIA is also looking at intelligence on a meeting of terrorist leaders in Iran the month before the crash to see if any green light was given for the attack. "There's a hard look being taken at the Iran possibility," says a senior U.S. intelligence official. However, he adds, the intelligence gathered so far is "vague, nothing solid." Even so, he says, it is "tantalizing."

FBI agents, working closely with intelligence agencies here and abroad, are scouring all incoming reports about a possible Iran connection. Of interest are the recent movements by an alleged Hizballah terrorist named Hussein Mikdad, who is purportedly backed by Iran. On April 4, Mikdad took a Swissair flight from Zurich to Tel Aviv with bomb parts hidden in a carry-on bag. Eight days later, Mikdad blew off both his legs and one arm when a bomb he was assembling in an east Jerusalem hotel room accidentally detonated. Israeli security officials believe Mikdad was building the bomb using a powerful plastic explosive called RDX and planned to place it aboard a flight leaving Ben Gurion Airport. This was the first known time that Hizballah slipped an operative into Israel by way of an international airline. FBI agents are planning to travel to Israel to study Mikdad's methods for any telltale bits of bombcraft that may be traced to TWA Flight 800.

The Iranian links to terrorism were further highlighted last week when Defense Secretary William Perry, in a National Public Radio interview, hinted that an ongoing Saudi investigation of the June 25 bombing of a U.S. military complex in Dhahran may "possibly" point to Iran's involvement. He suggested that the U.S. might have to consider "strong action."

In the TWA Flight 800 case, federal points of inquiry already assume the existence of a crime. If there was a bomb, did it contain Semtex, a powerful Czech explosive used by Libyan agents in the Pan Am 103 bombing? Or a lower-grade nitroglycerine-nitrocellulose mix? And what evidence can be extrapolated from the existing clues to help answer these questions?