Ramin Pourandarjani, 26, was based at Kahrizak, a prison on Tehran's outskirts where hundreds of opposition protesters were taken after being arrested in the crackdown following June's disputed presidential elections.
He died in mysterious circumstances on November 10, weeks after telling a parliamentary committee that a protester he had treated at the facility had died from heavy torture.
Authorities in Iran had initially claimed that Pourandarjani was killed in a car accident before suggesting that a heart attack or suicide was the cause.
However, Abbas Dowlatabadi, Tehran's public prosecutor, claimed that the young physician died from an overdose of propranolol – a drug used to treat high blood pressure and lower heart rate – in a takeaway salad.
Last week, Iran's top police commander, Ismail Ahmadi Moghaddam, insisted the death was a suicide, saying the doctor faced charges over failure to fulfil his duties to treat the detainees and killed himself in despair in a lounge at the courthouse. The police chief said a note was found with the body.
Opposition supporters have claimed that Pourandarjani was killed because he knew the conditions of a number of torture victims at Kahrizak, including 24-year-old Mohsen Rouhalamini, the son of a prominent conservative figure.
Hundreds of protesters and opposition activists were arrested in the crackdown that suppressed protests following the disputed June 12 presidential election. The opposition says at least 69 people were killed while the government has confirmed around 30 deaths.
More than 100 protesters, activists and pro-reform opposition have been on trial, accused of fuelling the protests and being part of a plot to overthrow the government.