The man beaten in a lift at Joliot-Curie metro station in Sofia was Assoc. Prof. Andrey Atanasov, 83, who taught for decades at the Faculty of Biology of Sofia University "St Kliment Ohridski".

At about 1pm on Thursday, 15 October, people saw the badly injured man and called 112. An emergency crew found him in a coma with multiple injuries and took him to St Anna hospital. He died later that day after medical treatment.

Sofia City Prosecutor's Office is supervising the pre-trial investigation into the murder, which Sofia police (SDVR) are leading.

Sources in the Interior Ministry say the suspect is a Greek national and is wanted. They say he left the scene in a rental car and then left Bulgaria. His identity and escape route have not been officially confirmed.

The sources say he is a younger man whom Atanasov had known for years. Their relationship soured after a personal conflict. No evidence about a motive has been made public. There is no information that he has been charged.

Investigators are checking whether he stalked Atanasov around the metro station for two days.

Police are analysing security camera footage, which is among the main material in the case. It shows the attack began before the lift and continued inside it. The suspect was filmed in a peaked cap with his collar turned up. On earlier visits to the area he also wore a medical mask.

A blunt object may have been used, given the severe head injuries. Heavy blood loss has been named as the cause of death, but no forensic medical finding has been released yet.

Atanasov worked in the Department of Biophysics and Radiobiology, set up in 1972. He researched proteins and biological membranes and specialised in biophysics in Germany and Japan.