Photo/Illutration Knives and plastic bags containing chunks of meat discovered inside an apartment in Ota, Gunma Prefecture, where four Vietnamese technical intern trainees lived are seen on Oct. 28. (Kaho Matsuda)

MAEBASHI, Gunma Prefecture--Four Vietnamese men who entered Japan as technical intern trainees were arrested on suspicion of illegally slaughtering a pig in their apartment in the prefecture, police said Oct. 28.

Gunma prefectural police plan to investigate the four in connection with a recent large-scale string of livestock thefts in the northern Kanto region. 

Those arrested are Cao Xuan Tung, 27, Nguyen Van Ngoc, 32, Tran Viet Hao, 22, and Nguyen Dung Hop, 32. They lived in an apartment in the city of Ota.

Police did not make it clear whether they admitted to the allegation of slaughtering the pig.

They are suspected of butchering the swine at their apartment around July.

The slaughterhouse law prohibits an individual from slaughtering a cow or a swine at a place other than a slaughterhouse unless they gain permission from the prefectural governor in advance for personal consumption of the meat.

The suspects are facing up to three years in prison or a fine of up to 3 million yen ($28,700) if convicted.

Police said they arrested Tung in a field in Ota on Oct. 4 on the suspected robbery of five gourds.

During the investigation, police found that the suspect's apartment resembled an image posted on social media as one believed to be linked to a number of livestock thefts reported in northern parts of the Kanto region.

Officers discovered butcher knives and many plastic bags containing pork in their apartment when they searched there.

They rearrested Tung on suspicion of violating the slaughterhouse law on Oct. 22. The three others were arrested on Oct. 28 on suspicion of illegally slaughtering.

A woman who lived near their apartment said their door always remained closed even in summer when it was the norm for most residents to keep their doors open.

Another resident said the Vietnamese men were often seen drying sheets.

Police will be looking into the men’s possible involvement in a series of agricultural-related thefts in the northern Kanto region with the losses estimated at more than 30 million yen.

Gunma Prefecture reported thefts of 719 swine, one cow and 144 chickens while Saitama Prefecture said eight goats, about 130 swine and 80 chickens were stolen. Tochigi Prefecture reported the theft of six cows.

(This story was written by Kaho Matsuda, Tsuin Cho and Hisao Nagata.)