Research has failed to find traces of the bug blamed for the Black Death, amid claims it may not be responsible.
Off the hook? Not quite.
The plague which wiped out 25 million Europeans in the Middle Ages has traditionally been blamed on a bacterium carried by rat fleas.
But UK scientists looked for DNA of the bug Yersinia Pestis preserved in victims' teeth - and found none.
However, this is still not enough evidence to prove the bug's innocence, reports New Scientist magazine.
The researchers, from Oxford University and Barts and the London Hospital, were responding to claims by a French team to have isolated fragments of Yersinia pestis DNA in teeth taken from the remains of disinterred plague victims.
The researchers looked in teeth because, in theory at least, the enclosed contents of the tooth might not perish over the centuries in the same way as other body tissues.
The fact that each tooth has its own blood supply might mean that high levels of plague bacteria in a dying patient might leave DNA traces behind.
The British researchers aimed to reproduce the French results to make sure they were not a freak event, perhaps caused by contamination in the laboratory.
They used teeth taken from skeletons dug up from "plague pits" at East Smithfield and Spitalfields in London. They also received samples from Copenhagen, and Angers and Verdun in France.
Their results were presented to the Society of General Microbiology conference in Manchester this week.
None of the teeth contained a trace of Y. pestis, and the researchers say that the cause of the Black Death remained an open question.
Dr Michael Prentice, a medical microbiologist from Bart's Hospital, told BBC News Online: "This can't prove that the Black Death wasn't Yersinia pestis, just that we couldn't reproduce the results of the French team.
"Ancient DNA is a very difficult area - it may be that these techniques will never be enough to provide an answer."
One future possibility, he said, was to find a plague victim buried in the permafrost of the far north of Europe - this might have sufficiently preserved tissues to allow DNA tests to reveal bacterial DNA.
Alternative theories abound for a new culprit for the Black Death.
A book published recently suggested a virus of the same type as Ebola might be the only way to explain the ferocious onset of symptoms and swift death of plague victims.
Yersinia pestis is by no means an historical phenomenon - there are still frequent cases of plague in many countries of the world, although modern antimicrobial treatments are effective if given quickly.
Most people die without treatment, and even with treatment, up to one in five die.