Eight people were apprehended for attempting to steal oil from a public pipeline by digging an underground tunnel, police said Tuesday.

The police caught the suspects at the site of the tunnel in Cheongju, North Chungcheong Province in March after being tipped off by the National Intelligence Service, Daejeon Provincial Police Agency said on Tuesday.

The case was handed to the prosecution while the four suspects, including the 58-year-old leader, were detained.

The suspects dug a 9-meter tunnel measuring 78 centimeters high and 81 centimeters wide from the basement of a motel which they rented in January, the police said. The tunnel was 30 centimeters away from the pipeline when the scheme was foiled.

The suspects, who dug the tunnel under a busy road used by 66,000 vehicles daily, used only shovels and pickaxes to avoid making a noise.

The gang was aided by a former employee of Korea’s state-run pipeline operator Daehan Oil Pipeline Corporation, who was previously fired after being convicted of stealing oil from another pipeline.

The suspects confessed during the police investigation that they planned to sell the oil at two gas stations, according to local media reports.