Russian authorities have arrested two Moscow subway workers in a deadly train derailment that killed 21 people on Tuesday.

The two men – track supervisor Valery Bashkatov and assistant supervisor Yury Gordov – stand accused of failing to properly oversee the replacement of a track switch mechanism in an underground tunnel in May, the Investigative Committee of Russia said. Bashkatov and Gordov will likely face criminal charges, the BBC reports.

An investigation found that workers used inadequate wiring to repair the switch mechanism, a misstep that ultimately resulted in a power surge that caused the train to derail. Besides the 21 fatalities, the accident left 162 people injured.

“The switch mechanism was fixed with ordinary 3-mm wire, which snapped,” the Investigative Committee said in a statement.

More than 1,000 people were evacuated when the train derailed west of Moscow between Slavianski Boulevard and Park Pobedy stations, one of the metro’s deepest points, the BBC notes. Authorities do not believe that militants – who have attacked Russia’s public transportation systems in the past – were responsible for the accident.

On weekdays, Moscow’s metro system transports more than 9 million people around the city. Local citizens have reportedly criticized the authorities in the past for focusing on the expansion of the system rather than its maintenance.