American and Cambodian officials urged museums and private collectors on Monday to investigate the origins of their Khmer art to determine whether it had been looted, and the officials demonstrated the pervasiveness of such thefts at an event that celebrated the return of 30 antiquities to Cambodia.

Lined up behind the officials were seven masterpieces of the country’s ancient heritage, including a 10th-century sandstone statue, known as “Skanda on a Peacock,” that investigators say was stolen from a temple by a Khmer Rouge conscript and self-described looter in 1997.

The Cambodian government will also welcome back a five-foot-tall sculpture of a Hindu god, Ganesha, but the four-ton sculpture was represented only in a poster on Monday for fear that it would break elevators at the Manhattan offices of the U.S. attorney for the Southern District of New York.

Both objects were said to have been plundered from the archaeological site at Koh Ker, the capital of the ancient Khmer Empire.

The antiquities that are being repatriated, the officials said, were all trafficked by an organized looting network and sold in the Western art market through Douglas A.J. Latchford, a British art dealer and collector of Cambodian antiquities. He died in 2020, less than a year after he had been charged with smuggling looted relics and concealing their tainted histories by falsifying documentation to help sell them.

“It’s like a returning of the souls of our culture back to our peoples,” Keo Chhea, Cambodia’s ambassador to the United States, said at Monday’s news conference.

The relics were returned as part of an investigation into Mr. Latchford by federal prosecutors in New York and the Department of Homeland Security. They were seized from two individuals and an American museum that had owned the artifacts. All three cooperated with investigators.

“We commend individuals and institutions who decided to do the right thing,” said Damian Williams, the U.S. attorney for the Southern District, “and after learning about the origin of the antiquities in their possession decided to voluntarily return those pieces to their homeland.”

The owner of “Skanda on a Peacock,” which depicts the Hindu deity Skanda riding the bird, inherited the sculpture from a collector who had purchased it from Mr. Latchford in 2000 for $1.5 million, according to court papers. The heir, who has not been publicly identified, agreed to relinquish possession of the artifact to the federal authorities.

Twenty-five of the antiquities that are being returned to Cambodia were surrendered by James H. Clark, the internet pioneer and Netscape founder who said he had spent roughly $35 million in purchasing dozens of Cambodian and Southeast Asian antiquities, many of which he used to furnish a Miami Beach penthouse.

“One day I recall walking through my apartment looking at these objects and thinking, ‘They really should be in a museum, and not in private hands,’” Mr. Clark said in a phone interview on Monday. “And that’s where they will be.”

Federal officials have said that Mr. Latchford duped Mr. Clark into believing the artifacts were being legitimately sold and that once they laid out evidence to the contrary, Mr. Clark agreed to surrender 35 items, most of which had origins in Cambodia. Those items include the elephant-headed Ganesha, a bronze seated Buddha and a sandstone Buddha.

The 30 artifacts cited on Monday are expected to arrive in Cambodia by October, after which the government hopes to have a national celebration around their return, said Bradley J. Gordon, a lawyer representing the country. Government officials intend for the items to ultimately be put on public display, he said.

Four of the antiquities were surrendered by the Denver Art Museum. The museum declined to comment on the ceremony but said it was also currently researching two objects from Thailand that were related to Mr. Latchford.

The criminal case against Mr. Latchford has been dismissed since his death. When he was alive, Mr. Latchford, who had been lauded by the Cambodian government for his scholarship on Khmer art and his contributions to state museums, had argued that Westerners who bought such antiquities and sold or donated them to museums were saving them from potential destruction.

At the ceremony Monday was a delegation of Cambodian officials who have been traveling across the United States for 10 days, visiting museums in California, Texas, Pennsylvania and New York to ask for documentation relating to the Khmer collections at the institutions.

Their efforts are part of a global push to recover hundreds of Khmer and pre-Khmer artifacts that made their way around the world as a result of decades of looting. Their mission has been furthered significantly with the help of a Cambodian man named Toek Tik, the former Khmer Rouge conscript, who has disclosed details of his prolific looting career to the authorities as a way to redeem himself for actions he now regrets.

Sopheap Meas, the deputy director of antiquities management at the Cambodian Ministry of Culture and Fine Arts, said that during her travels she had seen many one-of-a-kind objects that she believes should never have left Cambodia.

“The burden of proof should be on the museums to show that they have the right to legally own Cambodia’s national treasures,” she said.

The overarching message of the event, according to officials from both the United States and Cambodia, was that even though these objects were being repatriated, many more with illicit origins remained in the hands of private collectors and museums. Mr. Williams encouraged “anyone out there who believes that they have illegally obtained Cambodian or other antiquities in their possession to come forward.”

“We know that this problem goes much further, deeper than the activity of one man,” Mr. Chhea said.