ROME — Inside a chapel on the edge of Rome, a nun uses a key to open a wooden wall panel, revealing a hidden niche. Behind glass and stitched loosely to supporting backing hangs a relic of holy suffering: the bullet-pocked, bloodstained undershirt that John Paul II was wearing when a gunman shot him in St. Peter’s Square.

The short-sleeved garment bears the initials “JP,” sewn in red cotton thread on the label by nuns who did his laundry. Jagged rips run down from the neck and sides, made when emergency room staff tore open John Paul’s shirt as they raced to save the 60-year-old pontiff’s life.

It’s one of the most remarkable of the endlessly surfacing relics of John Paul, who will be declared a saint Sunday in the very same square where a Turkish would-be assassin shot him on May 13, 1981.

Relics of John Paul have enjoyed a boom ever since the beloved pope was beatified in 2011, and they are gaining heightened significance — as well as a surge of veneration — ahead of his canonization. The phenomenon has been fueled by John Paul’s longtime Polish confidant and secretary, Stanislaw Dziwisz, who doles them out to churches upon request.

The famous undergarment was discovered by the head nurse in the operating room at Rome’s Gemelli Polyclinic as she was cleaning the floor.

“She understood that the undershirt could be important,” said Sister Amelia Cicconofri, who displays the shirt at Regina Mundi church upon request.

Nurse Anna Stanghellini, who lived out her last years at the church’s convent, donated the shirt to the nuns there.

Relics of John Paul are by no means limited to Rome. John Paul was the world’s first globe-trotting pope, and he left things associated with him scattered around the globe. To qualify as a relic, an object needs only to have been in physical contact with the saint in question.

The Manila area restaurant where John Paul dined during his 1995 pilgrimage to the Philippines shows off the spoon, fork, water goblet, knives and table napkin — all still unwashed after his meal of grilled fish and fried shrimp. Elsewhere in the predominantly Catholic Asian nation, shopping malls are showing strands of his silvery-white hair and a piece of bedsheet from his deathbed.

The other pope to become a saint on Sunday — John XXIII — has not attracted anywhere near the relic frenzy of John Paul. John XXIII, who called the revolutionary Vatican II Council, only served as pope for 4½ years, and there are simply not that many objects associated with him.