Until the museum in Benin City is built, however, nothing is likely to be returned permanently unless it is done by individuals. No one has a firm idea how many looted items are in private hands, but they used to regularly come up at auction. (The record price, set in 2016, is well over $4 million.)

Mr. Dunstone said he had hoped that dozens of people would have come forward with items to return by now. The ceremony in 2014 received a flurry of media attention, and he went back to England expecting new Mr. Walkers to appear.

It didn’t happen. He got one email from a man in South Africa who claimed to have fished a Benin Bronze out of a river. He was willing to mail it to Mr. Dunstone for $2,500.

Mr. Dunstone, ever the police officer, suspected a scam and didn’t write back.

“I’m less proactive now,” he said. “But my heart’s still open.”

Mr. Awoyemi said he was disappointed, too, that no one came forward, but was excited by the museum plan. He was even willing to help with security, he said, if the oba would let him.

Mr. Walker can’t put the Benin Bronzes behind him, either. A few months ago, he was looking online at Benin Bronzes held by the Horniman Museum in London and came across an intricately carved wooden paddle. It was almost identical to two he had in his home, which he thought his parents had bought on vacation.