Oklahoma City, Okla. (CNA/EWTN News) -- When Father Stanley Rother, a missionary priest from Okarche, Oklahoma, was killed by rebels in Guatemala, his body was transferred back to the United States to be buried by his family.

But his heart remained in Guatemala.

Literally.

The native Guatemalans loved their pastor so much that they enshrined his heart at the mission parish in Santiago Atitlan.

On Sept. 23, that heart will go from being a disembodied remain to a first-class relic, a sacred artifact of someone who has been beatified by the Catholic Church.

The keeping and venerating of relics is perhaps one of the more bizarre Catholic practices, but it's a scripturally-backed practice of the Church since its beginning.

There are three classes of relics recognized by the Church. First-class relics are bodily remains of a saint, such as bones or flesh or hair. Second-class relics are belongings of the saint, such as clothes or other personal items. Third-class relics are items that have been touched to a first- or second-class relic of that saint.

When Archbishop Paul Coakley was installed as head of the Oklahoma City Archdiocese in 2011, he inherited the task of the cause of canonization for Father Stanley Rother. As part of this undertaking, he also inherited the task of his gathering relics, a process that officially commenced once it was clear that the martyred priest's beatification was imminent.

The second-class relics were easy. Over the years, the archdiocese had collected a handful of personal items of Father Stanley, donated by friends and family, including some of his clothes, and a pipe that he smoked. Once he is beatified, these things become second-class relics.

But when it came to exhuming the body to collect first-class relics, Archbishop Coakley admits he was a little lost.

"We had to do a lot of research," the archbishop told CNA. "This happens so rarely, we didn't know how to go about preparing for this."

First, he obtained permission and rights to Father Stanley Rother's remains from the priest's two surviving siblings.

Then, according to Vatican protocol, he gathered the prescribed team of witnesses and medical experts who would help with the canonical exhumation and examination of Father Stanley's body.

The medical team consisted of a pathologist and an orthopedic surgeon, both local Catholics. They helped examine and describe the remains, and compile a report sent to the Holy See. Among other things, the Church looks for signs of incorruptibility, when a body does not decompose. The condition has been found among some saints, although by itself, it is not enough to prove sanctity.

"They had expertise that would be helpful in describing what would be found when his tomb was opened, because we didn't know what we could find," Archbishop Coakley said.

Both the exhumation and examination are done "with great dignity and reverence, and there is a process by which we exhumed his body from the family plot at the parish cemetery in Okarche," the archbishop added.

"And in that process we took one of his ribs, and that's what we used for preparing first class relics," he said.

His body was then transferred to a temporary resting place in Resurrection Cemetery, a Catholic cemetery next to the pastoral center in Oklahoma City, while his rib was sent to Rome.

"There is an Augustinian monastery of St. Lucia in Rome, and they are custodians of relics and have experience in preparing relics, so we sent our relic of Father Rother to them," Archbishop Coakley said.

The sisters there will divide the rib into many tiny fragments, which will be encased in reliquaries, available to bishops who wish to obtain relics of Father Rother for public veneration. First-class relics are no longer distributed to lay persons, in order to protect the relics from negligence or abuse.

Meanwhile, the task of preparing the third-class relics (sometimes referred to as "touched relics") of Father Stanley fell to the Carmelite Monastery of Rochester, New York, a congregation of 11 discalced, cloistered Carmelite nuns.

Mother Therese, the prioress of the convent, told CNA that while the sisters had done smaller "touched relic" projects for Carmelite saints, this was the first major relic project the convent has undertaken.

"A sister from Oklahoma City mentioned to me that the archdiocese was looking for someone to put together relic cards for Father Stanley's beatification," she said. "I said, 'Well we've not done this on a huge scale but we are familiar with this process'...so that's how it came about, a simple question from one of our Carmelite nuns."

Often, third-class relics distributed at beatifications come in the form of a little piece of cloth embedded in a holy card.

"When the body was exhumed, the bones were wrapped in a very large and special cloth," Mother Therese said.

This cloth was signed and dated by Archbishop Coakley during the exhumation in May and then sent to the nuns, who are punching small holes in the holy cards of Father Stanley and affixing the pieces of cloth -- which will become relics once Father Stanley is beatified -- to the cards.

The holy cards also have a picture of Father Stanley on the front, and a prayer for his canonization on the back -- some in English and some in Spanish. The sisters have already made 10,000 and are expecting to make several thousand more.

"It's a very great privilege for us," Mother Therese said. "It has brought us very close to Father Stanley...we feel that he will intercede for us and that he will bless our community and the Church in the U.S. as well, because he's the first American-born martyr."

Archbishop Coakley said working on Father Stanley's cause has been an honor, especially as someone who graduated from the same seminary as Father Stanley (though years later) and has been interested in his story for quite some time.

"I took that as a great privilege to be coming into the Oklahoma City Archdiocese at such a time," he said.

"I...entrusted my ministry to him and prayed for his assistance and intercession as I undertook this ministry, I've felt a very near kinship with him since I was a seminarian and a priest and as the archbishop now."