Rings with gems and crosses made of precious metal were stolen from the home of Archbishop John Nienstedt, the head of the Archdiocese of St. Paul and Minneapolis, in a well-planned heist executed early on Saturday.

"These things are historically and reverentially irreplaceable," the archdiocese spokesman, Dennis McGrath, said Monday, according to the Associated Press. "They're beyond value."

Archbishop Nienstedt was in Rome at the time of the robbery receiving his pallium from Pope Benedict XVI.

Police spokesman Peter Panos said the thief or thieves climbed onto a first-floor roof and then broke into a second-story window of the archbishop’s home.

"These guys were pros," Panos said. "The glass they broke through is like three or four inches thick. They couldn't get through without a sledgehammer. They executed a well-thought-out plan. They knew exactly where to go in his bedroom.”

In addition to the rings and crosses, rosaries and a small safe are believed to be missing.