From the Telegraph:
Alfredo Barbagallo, an Italian archaeologist, claims that it is buried in a chapel-like room underneath the Basilica of San Lorenzo Fuori le Mura, one of the seven churches which Christian pilgrims used to visit when they came to Rome.
Mr Barbagallo based his claim on two years spent studying mediaeval iconography inside the basilica and a description of a particular chamber, in a guide to the catacombs written in 1938 by a Capuchin friar named Giuseppe Da Bra.
The friar describes a room of about 20 square metres with a vaulted roof ceiling. "In the corner of a wall-seat there can be seen a terracotta funnel whose lower part opens out over the face of a skeleton," he wrote.