Police are stepping up an investigation into South Korea's single largest embezzlement case that has engulfed a local medical equipment producer, officers said Thursday, following the arrest of a suspect the previous day.

A 45-year-old employee of Osstem Implant Co., identified only by his surname Lee, was arrested at his residence in Paju, 30 kilometers north of Seoul, on Wednesday on charges of embezzling 188 billion won ($157 million) from the dental implant maker.

The arrest came just five days after the company filed a complaint against Lee, but the whereabouts of the embezzled money equivalent to over 90 percent of the company's equity of 205 billion won as of end-2020 are yet to be known, police officers said.

The police are also working hard to find out if there were any accomplices who helped Lee during his crime and escape.

Osstem has repeatedly emphasized that Lee had acted alone, but police suspect that the fund was too big to be stolen by a single team leader-level employee like him.

Lee has already admitted to embezzlement, according to the police officers.

Police have so far confirmed that Lee had purchased stocks and 851 1-kilogram gold bars estimated to be worth 68 billion won from the Korea Gold Exchange from Dec. 18-28.

Police have failed to secure all of the gold bars bought by Lee, though some of them were confiscated from his home during his arrest.

But the estimated prices of all the gold bars and stocks allegedly bought by Lee reportedly reach up to only tens of billions of won and the whereabouts of the full amount of embezzlement still remained unknown.

Police are also puzzled as to why Lee bought gold bars that are relatively easy to track and was hiding in his home that was within their surveillance network.

Police say it is unusual for an embezzlement suspect anxious to avoid the surveillance of the investigation authorities to buy a large amount of heavy and bulky gold ingots.

Moreover, Lee personally visited the gold exchange to buy gold bars, allowing investigators to easily track his whereabouts by analyzing nearby surveillance cameras. It is also questionable why Lee chose to hide in his home, instead of running far away.

Police said they plan to seek an arrest warrant for Lee later this week after conducting further questioning about all the doubts.

Police suspect Lee may have suffered a loss of about 30 billion won in the process of buying about 3.91 million shares in a listed company called Dongjin Semichem in October and reselling almost all of the stocks in December.

Lee is also said to have spent several billions of won to buy several real estate properties for his wife, younger sister and other relatives, and cancel lenders' rights to collateral security for the properties.

Established in 1997, Osstem Implant is the country's largest manufacturer of dental implants. The company also holds the largest market share in the Asia-Pacific region and is fourth in the global market. (Yonhap)