BOSTON — Thursday brought high drama to the trial of James (Whitey) Bulger, the reputed crime boss of South Boston. There was a new death amid so many old mob deaths. And his former partner took the stand, pointed a finger at Mr. Bulger and later accused him of being what he most fears being labeled — an F.B.I. informant.

The day began with reports that a jogger had found the body of Stephen Rakes, who until recently had been scheduled to testify against Mr. Bulger. It was a measure of the legacy of fear wrought by Mr. Bulger’s Winter Hill Gang that many who knew Mr. Rakes wondered about foul play, although the authorities said there was no evidence of it.

“I hope he wasn’t murdered,” said Steve Davis, the brother of a woman Mr. Bulger is accused of strangling, as he stood outside the federal courthouse where the trial is in its fourth week. “It brings you back to the early ’80s,” he said, referring to the frequent murders by Mr. Bulger’s gang.

Later in the day, a Bulger associate, Stephen Flemmi, took the stand for just a few minutes, but it was long enough for him to assert a couple of points devastating to the defense.