The Catholic Church was shocked last month when an ornate golden artefact said to contain drops of Jesus's blood was stolen shortly before an annual celebration in northern France.
For 1,000 years, pilgrims have headed to Fécamp abbey in Normandy to worship the "Precious Blood of Christ" relics.
Six weeks later, a Dutch art sleuth has described how the relics were handed over to him in an elaborate operation.
Arthur Brand says he will now give them to police to return them to the abbey.
"Seven to eight per cent of stolen art is returned and much of it is destroyed. In this case, I think the thief had no idea what it was," he told the BBC.
The relics were stolen late at night on 1 June from the sacristy at Fécamp, north-east of the port of Le Havre. The thief is believed to have been locked in the building overnight and there was little security at the time.
Mr Brand, who is widely known for his work in tracking down stolen art and artefacts, described how he was contacted by email by someone who revealed the relics had been stored at the home of a friend of the thief.
When the friend realised what it was, he then passed it on to the person who emailed the Dutch art detective, who suggested that they leave it on his doorstep and ring the doorbell.
Returning it direct to the abbey ran the risk of arrest, Mr Brand explained.
Le Havre Bishop Jean-Luc Brunin said at the time that it was an unbearable attack on people's faith and part of a tradition that stretched back to the 12th Century.
The theft took place less than two weeks before an annual Mass celebrating the "Precious blood" relic.
"A couple of days later, at 10:30 in the evening, the doorbell rang. I looked from my balcony outside and in the dark I saw a box. I ran down the stairs, afraid that someone would take the box. Outside I looked around, but there was no-one there," said Mr Brand.
As a Catholic himself, he said he could not believe the beauty of the relics, describing the moment he opened the box containing them as an "authentic, religious experience".
He said he would hand the relics over to Dutch police on Tuesday and they would be responsible for returning them to the abbey at Fécamp.
https://www.bbc.com/news/world-europe-62092195
