KOLKATA: A 30-year-old nurse was found dead under mysterious circumstances at the state-run NRS Medical College and Hospital in Kolkata, police said on Thursday.She was on night duty at the hospital’s high-dependency unit (HDU) on Wednesday, they said.According to the preliminary investigation, she reported for duty around 8 pm and went to the staff washroom at the antenatal ward in the Gynaecology Department Building around 10.30 pm, police said.“When she did not return for some time, her colleagues went to check on her and found the washroom door locked. After repeated knocks drew no response, two of them broke open the door and found her lying unconscious on the floor,” a police officer told news agency PTI.A doctor was called to examine the nurse, who was subsequently declared dead, the officer said.Personnel from Entally police station, along with officers from the Detective Department’s Homicide team, reached the hospital after being alerted about the incident.The preliminary investigation found no visible injury marks on the nurse’s body, while no suicide note was recovered, the officer said.“We suspect that the nurse may have died following an overdose of an anaesthetic drug administered through an injection. However, our detectives are investigating all possible angles,” he said.The nurse’s body has been sent for a post-mortem examination, the officer added.State health minister Sharadwat Mukherjee visited the hospital on Thursday morning and spoke to staff members who were on duty on Wednesday night.(With agency inputs)