An explosion occurred in the midst of a train traveling from Sennaya Ploshchad to Tekhnologichesky Institut in Moscow.

“In the metro car, everyone expected death, if I can say that. After the explosion, everyone expected consequences. Then we were taken out, and people began to help each other, brought others out. Most were covered in blood,” a passenger on the train told the state-run TASS news agency.

At least 51 people were injured in the attacks with 14 killed on the St. Petersburg metro on Mon., Apr. 4. According to Health Minister Veronika Skvortsova, four of the injured are in critical condition.

According to Russia’s Anti-Terrorism Committee, another larger device was found and defused at another station.

At that moment, no group has claimed responsibility for the incident. Thus, the city’s metro system was shut down.

“The reasons for the explosion are unknown, so it’s too early to talk about it. The investigation will show what happened,” said Russian President Vladimir Putin when beginning a meeting with Belarussian President Alexander Lukashenko.

On Tuesday, investigators from the Russian Investigative Committee identified the incident as a suicide bombing, claiming Akbarjon Djalilov guilty of the attack.

Putin, who has been in St. Petersburg earlier that day for a visit, laid roses at a memorial with candles outside of the bombed metro station.

The chairman of the defense committee in the Federation Council Viktor Ozerov claims that the location of St. Petersburg as a target for the attacks may have been tied to Putin’s visit.

“The choice of the place and the timing of these blasts is not accidental. The president of Russia is in St. Petersburg. The media forum is taking place there. There are many journalists,” Ozerov said to CNN.