After two years of study, in November 2012 they concluded that Tycho Brahe was not murdered, but most likely died of a burst bladder. An interesting article on the results of the study can be found at the UK's Guardian newspaper. As the article notes:
Brahe's death in 1601 at the age of 54 was long believed to have been due to a bladder infection. Legend said it was the result of his reluctance to breach court etiquette during a reception by leaving for a toilet. Kidney disease was another suspect. But some speculated that he might have been poisoned with mercury even at the hands of a king or a rival astronomer.
"Brahe's famous assistant [astronomer] Johannes Kepler has been identified as a possible murder suspect, and other candidates have been singled out for suspicion throughout the years," said Jens Vellev, a professor of medieval archaeology at Aarhus University, Denmark, who heads the Czech-Danish team of scientists that conducted the research.