The FBI set up shop at the home of a 91-year-old man near Indianapolis, saying he has thousands of artifacts and cultural items originating from at least a dozen different countries and Native American tribes – some of them acquired improperly.

Agents and scientists, working in tents erected outside the house last week, were taking items from the home of Donald C. Miller and packing them up for further analysis.

“I have never seen a collection like this in my life except at some of the largest museums,” said Larry Zimmerman, an anthropology and museum studies professor at Indiana University-Purdue University Indianapolis, who is helping the FBI figure out what’s in the private collection.

FBI agent Robert Jones last week declined to describe the artifacts found at Miller’s home. But he said they had been acquired over eight decades from various nations, including Australia, China, Haiti, Italy, New Guinea, New Zealand, Peru and Russia.

Some of the items had been “knowingly and unknowingly collected in violation of treaties and federal statutes,” Jones said. But some may have also been acquired before some restrictions went into place. The U.S. attorney’s office in Indianapolis will decide whether to file charges after the investigation is complete. That could take months, the FBI said.

The “fairly well-maintained” artifacts sat in several different structures on Miller’s remote property in Waldron, Ind., Jones said. The exact number and monetary value of the items is not yet known. But “the cultural value of these artifacts is immeasurable,” Jones said.

Officials collaborating with experts in various cultural fields were working under tents at the property to determine what each item is and how and when each was acquired. Items that don’t lawfully belong to Miller would be returned to the proper foreign and Native American authorities, Jones said.

“A great deal of effort has gone into making sure each and every object is respected and handled with the utmost professionalism,” said Holly Cusack-McVeigh, another museums and anthropology professor with Indiana University-Purdue University. She too is assisting in the case.

Authorities descended on the house last week after several months of investigation. Jones said an art crimes expert at the FBI’s Indianapolis office had received information that Miller was hoarding items that “needed re-repatriation.”

The FBI’s large presence at the home early Wednesday drew media attention and the agency said the extensive number of items at Miller’s home warranted the size and scope of the law enforcement presence.

Most requests to open artifact investigations come from special police units in other countries, said Ioanna Kakoulli, an associate professor of archaeological science at UCLA who helps the U.S. Department of Homeland Security in such cases.

“You really need to look at every lead you have,” she said in an interview. “Cultural heritage is not a renewable resource, so it’s worth protecting.”

Authorities said Miller has traveled extensively and that he is cooperating with the investigation and is in good health.

Miller’s collection had been featured in local media reports several years ago. He described himself as a World War II veteran who later worked on the atomic bomb project in New Mexico. His collection stretched from ancient Chinese pottery to recent discoveries of Native American tools, according to the reports. Miller could not be reached for comment.