Few German thrillers have been able to match the stranger-than-fiction case of Uwe Barschel, former premier of the north German state of Schleswig-Holstein, who was found dead in a Geneva hotel bathtub in October 1987.

Although Barschel's death by drug overdose was ruled a suicide, the unanswered questions surrounding the case have long provided grist for conspiracy theorists and amateur gumshoes eager to prove the 43-year-old conservative politician was assassinated.

Now German authorities have fanned the flames by reopening a murder investigation, partly as the consequence of documents unearthed from East German security files and unspecified information from Germany's federal intelligence agency. Federal and state investigators are to meet on Jan. 13 to compare clues and theories. Their goal is to determine whether, as the prosecutor averred in reopening the case two weeks ago, there is "sufficient evidence of involvement of a third party" in Barschel's death.

Who that "third party" might have been remains a mystery, as does a plausible motive for murder. Among suspects bandied about in what Der Spiegel magazine calls "the greatest political crime story in postwar Germany" are Israeli intelligence agents, an Iranian hit squad, disgruntled gunrunners and killers working for the Stasi, which was East Germany's secret police. One recent headline even asked, "Was Barschel's Bathtub Filled by the CIA?"

Another theory holds that a cunning if despondent Barschel indeed killed himself but deliberately invested the act with enough curious circumstances to suggest foul play. This, the theory goes, was an attempt to turn himself into a victim and clear a name besmirched by political scandal.

That Barschel had been disgraced shortly before his death is beyond dispute. The father of four and a rising star in Chancellor Helmut Kohl's Christian Democratic party, the young politician found his career abruptly in ruins when he resigned as premier -- the equivalent of a state governor -- on Sept. 25, 1987. Two weeks earlier, one of Barschel's press aides had publicly accused him of hiring a private detective to gather damaging information about a political opponent's sex life; Barschel allegedly authorized other dirty tricks, including the writing of an anonymous letter accusing the opponent of tax fraud.

Barschel vehemently denied involvement in the scandal, but corroborating evidence suggested his complicity, and his political allies deserted him. After resigning, he took a vacation in the Canary Islands and then, on Oct. 10, flew to Geneva. There, his widow subsequently said, he hoped to meet a mysterious informant named Robert Roloff, who supposedly had evidence impugning the accusatory press aide and exculpating Barschel.

Whether Roloff ever existed is unclear. The next day, Oct. 11, a reporter looking for Barschel went to room 317 in the posh Beau Rivage Hotel. Finding the door ajar, he pushed inside to find the former premier, fully clothed, dead in the drawn bath. An autopsy and inquest concluded that he had died of a self-administered combination of sleeping pills, including a lethal dose of the barbiturate cyclobarbital.

Mysteries remained, however. Unidentified fingerprints and palm prints were found in the room. No trace was found of the bottle of Beaujolais wine brought to the room the previous night by a room service waiter. A prominent Swiss forensic toxicologist asserted -- and has recently repeated his contention -- that the pills which killed Barschel had been ingested after he was rendered helpless by a dose of sleeping tablets, arousing suspicions that Barschel had been sedated and then poisoned.

Despite contentions by Barschel's family that he was murdered, interest in the case subsided until 1993 when it was disclosed that the press aide who had brought the premier down had been on the payroll of the political opposition. More sinister in some minds are Stasi documents allegedly implying that Barschel had been secretly meeting with Iranian and Israeli agents and was under surveillance by the CIA and West German intelligence.

One Stasi document published recently by the daily Berliner Zeitung reportedly cites a CIA cable intercepted by East German intelligence. Dated shortly before Barschel's death, the cryptic message seems to refer to Barschel as "Perch," the English translation of his name: "Jerry took Perch to temple, met with Lokal and Rabbi at 2130. Perch unyielding, refuses coop."

German government officials contend the cable is probably phony, concocted by either the Stasi or the Soviet KGB as a means to embarrass Bonn or Washington. Fake or real, the Stasi papers -- combined with the recent reopening of the case -- have spawned half a dozen theories about who killed Barschel.

One hypothesis is that Barschel was killed by vengeful Iranian hit men after he intervened on behalf of a Kiel shipyard owed 250 million marks ($160 million) by Tehran for work on a submarine project. Another theory -- formally denied by the Israeli government -- is that the Mossad secret service killed him after he refused to support the secret training of Iranian pilots near the Schleswig-Holstein state capital of Kiel, a project supposedly endorsed by Israel as a means of keeping Iran and Iraq at each others' throats.

Still other theories hold that Barschel was involved in illicit smuggling -- either of guns or nuclear materials -- from Sweden to India and Pakistan, and was killed because he knew too much. And there is the Stasi-did-it hypothesis, supposedly after the anti-communist Barschel realized that the East Germans had engineered his political demise or because he had learned too much about East German gunrunning.

If all of these theses are unified by their lack of proof -- some would say coherence -- they nevertheless have taken root in the imagination of the German public. With so many suppositions and accusations now afoot, the authorities find themselves in the difficult position of determining whether a prominent politician who died seven years ago was really the victim of a diabolical plot -- or the creator of a posthumous puzzle.

CAPTION: UWE BARSCHEL