WASHINGTON — His decades-long obsession with a college sorority may link a former Army biowarfare scientist to four anthrax-laced letters dropped off at a New Jersey mailbox in 2001, authorities said yesterday in the latest twist of one of the most bizarre unsolved crimes in FBI history.

U.S. officials said Bruce Ivins’s fixation with Kappa Kappa Gamma could explain one of the biggest mysteries in the case: why the anthrax was mailed from Princeton, N.J., 195 miles from the lab it’s believed to have been smuggled from.

Still, authorities acknowledge they cannot place Ivins in Princeton the day the anthrax was mailed. And the curious explanation connecting the scientist and a sorority is unlikely to satisfy his friends and former co-workers who question what motive the married father of two might have had for unleashing the attack.

Ivins, 62, killed himself last week as the Justice Department prepared to indict him on capital murder charges for the deaths of five people who were poisoned by the anthrax in the weeks following the terrorist attacks of September 11, 2001. His attorney maintains he would have been proven innocent were he still alive.