Russian authorities have detained two Moscow subway workers over the fatal subway derailment that killed at least 21 people and injured over 150 others.
Russia's major investigative agency says the senior Moscow roadmaster of railway service, Valery Bashkatov, and his assistant, Yury Gordov, have been questioned and authorities are preparing to formally charge them with safety breaches.
The investigative committee says high-ranking officials could also be arrested, as authorities intend to probe everyone involved in the subway crash.
The incident happened during the morning rush hour on Tuesday when the train braked suddenly and ran off the tracks between two stations.
The investigative committee says that the cause of the crash was a improperly installed rail switch and the snapping of a single 3-millimeter wire. Another subway line is currently in construction near the site of the crash, and the rail switch was intended to direct the trains around the construction site.
Baskhkatov and Gordov were in charge of overseeing the construction between the two stations as well as the safety standards of the subway.