A 26-year-old doctor who exposed the torture of jailed protesters in Iran died of poisoning from a delivery salad laced with an overdose of blood pressure medication, prosecutors say. The findings fueled opposition fears that he was killed because of what he knew. Investigators are still trying to determine whether his death last month was a suicide or murder, Teheran's public prosecutor Abbas Dowlatabadi said, according to the state news agency IRNA. The revelations of torture against prisoners in Iran's post-election turmoil angered even government supporters and deeply embarrassed the country's clerical leadership and security forces. Much of the abuse took place at Kahrizak, a prison on Teheran's outskirts where hundreds of opposition protesters were taken. Several there died, and the facility became so notorious that Iran's supreme leader was forced to close it down. Ramin Pourandarjani, a doctor at Kahrizak, later testified to a parliamentary committee and reportedly told them that a young protester he treated died from severe torture. He said he was also forced by security officials to list the cause of death as meningitis, according to opposition Web sites. Pourandarjani died on November 10 in mysterious circumstances, with authorities initially saying he was in a car accident, had a heart attack or committed suicide. Forensic tests showed that the doctor died of "poisoning by drugs" that matched doses of propranolol found in a salad that was delivered to him, Dowlatabadi said Tuesday. "A large number of these pills must be used for a person to pass away from them," he said. Propranolol is used to treat high blood pressure, rapid heart rate and tremors, and can be lethal in high doses. The restaurant delivery man told investigators that he gave the salad directly to Pourandarjani and described how the doctor took it from him at the door of his room, then closed the door behind him, Dowlatabadi said. The delivery man is not under arrest, he said. Last week, Iran's top police commander, Ismail Ahmadi Moghaddam, insisted the death was a suicide. He said the doctor faced criminal charges over failure to fulfill his duties to treat the detainees and killed himself in despair in a courthouse lounge. The police chief said a note was found with the body. But the police chief, speaking more than a week after the death, only highlighted the mysteries. His comments were the first and only public word that Pourandarjani had faced any charges - or that he had died in a courthouse. The IRNA report on the prosecutor's announcement did not say where the doctor was when the salad was delivered to him. One pro-reform lawmaker dismissed the claims and suggested a link to the prison torture. "It is impossible to accuse him of suicide," said Masood Pezeshkian, the pro-opposition Web site Roozonline reported Wednesday. "The idea of suicide by someone who had no problems and no serious disease - and was present during the events at Kahrizak - seems questionable to us." The doctor's father, Reza-Qoli Pourandarjani, told The Associated Press last month that he didn't believe any of the causes of death given so far by the government. But he didn't go as far as accusing anyone of killing his son. "Just the night before his death, my child talked to me on the phone, it was around 8 or 9 p.m. He sounded great, very dignified, displaying no sign of someone about to commit suicide," he said in a telephone interview from his home in Tabriz in northwestern Iran. "He was even full of hope" and making plans with friends, the father said. The next day, the elder Pourandarjani received a call from a Teheran security official informing him that his son was in a car accident with a broken leg and needed his consent to have surgery. When he traveled to Teheran, "we found out that that wasn't the case," the father said. Several opposition Web sites raised concerns that Pourandarjani was killed because he knew details on a number of torture victims at Kahrizak, including 24-year-old Mohsen Rouhalamini, the son of a prominent conservative figure. Rouhalamini's death in late July was the main factor raising anger among government supporters over the abuse. In his testimony, the doctor told the committee investigating abuse that Rouhalamini was brought to him at Kahrizak "in a dreadful state after being subjected to extreme physical torture. He was in a critical state," the opposition Web site Mowjcamp said, citing parliament officials. Pourandarjani said that after the youth's death, "officials in Kahrizak threatened that if I disclosed the causes of the wounds of the injured at Kahrizak, I would not be able to live," the site reported. Hundreds of protesters and opposition activists were arrested in the crackdown on protests following the disputed June 12 presidential election, in which the opposition says President Mahmoud Ahmadinejad's victory was fraudulent. 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 fueling the protests and being part of a plot to overthrow the government.