The Vatican's top art historian on Monday shot down a report in its own newspaper that suggested a recently discovered painting was a Caravaggio.

The head of the Vatican Museums, Antonio Paolucci, wrote in the Vatican newspaper L'Osservatore Romano that the work was most likely a copy of an original by a Caravaggio-influence artist.

It was L'Osservatore itself that set the art world aflutter last week with a front-page article headlined "A New Caravaggio," detailing the artistry behind the "Martyrdom of St. Lawrence," which had been discovered in the sacristy of a Jesuit church in Rome.

The author of the article, art historian Lydia Salviucci Insolera, had made clear that she was not making any conclusions about the authenticity of the work and that more diagnostic tests were required....