A U.S. appeals court on Wednesday overturned the conviction of a former Chinese diplomat and head of U.S. operations for a Chinese construction company for engaging in forced labor, while upholding his conviction on two other charges.

Citing improper testimony from a government expert on forced labor, the 2nd U.S. Circuit Court of Appeals in Manhattan ordered a new trial for Dan Zhong on three counts related to his allegedly having forced workers into "debt bondage" contracts.

Zhong, 52, has been serving a 190-month prison term--nearly 16 years--following his March 2019 conviction, including concurrent nine- and five-year terms for alien smuggling and visa fraud.

Wednesday's decision upheld those convictions, but ordered a resentencing on the visa fraud count.

The office of U.S. Attorney Breon Peace in Brooklyn declined to comment. Lawyers for Zhong did not immediately respond to requests for comment.

Zhong had overseen U.S. operations at privately held China Rilin Construction Group, led by his uncle Wang Wenliang, a onetime billionaire, according to Forbes magazine.

Prosecutors alleged that from 2010 to 2016, Zhong brought Chinese workers to the United States on visas, purportedly to work on diplomatic facilities including China's U.N. mission, embassy and consulates general.

Instead, prosecutors said Zhong compelled them to work on private construction projects, or perform yard work and cooking at his New Jersey residence, and threatened them with the loss of their homes in China if they refused.

The appeals court said the expert witness' "color commentary" about the government's evidence came "dangerously close" to cementing Zhong's guilt, and that he gave largely irrelevant testimony about forced labor worldwide and the Chinese government's "poor" forced labor record.

It also said jurors should not have heard testimony about Rilin's alleged treatment of three workers in 2001 and 2002, many years before Zhong's alleged crimes.

"We cannot conclude that the cumulative effect of those errors was harmless," Circuit Judge Steven Menashi wrote for a three-judge panel.

Zhong has been in U.S. custody since his November 2016 arrest. He is housed at a federal prison in West Virginia.

The case is U.S. v. Zhong, 2nd U.S. Circuit Court of Appeals, No. 19-4110.