But we do know where it turned up: in the Tel Aviv apartment of Oded Golan, an Israeli entrepreneur, amateur pianist, and one of the world's biggest collectors of biblical antiquities. He says he bought the ossuary from an Arab dealer in the 1970s and never thought twice about the inscription, because, as a Jew, he knew nothing about Jesus.
"I didn't know at the time at all the Jesus had any siblings," says Golan, who says he had the ossuary for more than 25 years and didn't know the potential significance of it.
It was only in 2002, Golan says, that an eminent scholar happened to see the ossuary at his home and told him what the writing could mean. Golan sprung into action. He had the box scrutinized by specialists in different fields. They were impressed. So Golan shipped it off to Toronto for its unveiling before a colloquium of archaeologists, who gave it their undivided attention.
After they'd had their fill, the Israeli antiquities authority demanded that it be brought back to Israel so they could have a look. They appointed two committees to decide whether that inscription was cut 2,000 years ago, or much more recently. Their conclusion: it was a fake.
The ossuary was returned to Oded Golan. But then, just two months after it had been exhibited in Toronto, there was another extraordinary revelation: a tablet was secretly offered to Israel's National Museum with a reported price tag of $4 million.
Why so much? It was billed as the only remnant of the temple of King Solomon - a godsend for religious Jews, because it would strengthen their claim to the Temple Mount, which has been contested for centuries by Jews and Muslims.
First the ossuary, then the tablet, both revealed in the space of two months. An amazing coincidence. But the amazing coincidences don't stop there.
Amir Ganor, head of the Antiquities Authority Detective Unit, was put on the tablet's trail. All leads pointed to the same address in downtown Tel Aviv: Oded Golan's apartment.
They confiscated the tablet and decided to take the ossuary as well. But when Golan led them to it, these detectives could barely believe their eyes. "He opened a small chamber on the roof, and I saw this chamber is a toilet and what I found on top of the toilet, I found the ossuary of James the brother of Jesus," Ganor recalls.
Golan doesn't try to deny that he kept the ossuary on the toilet, but he urges: don't leap to unwarranted conclusions. "I was really scared that people will come into the house and steal it, so I took it to the safest place in this building," he says.