Lin Senhao, former student at Fudan University, stands the second trial at Shanghai High People's Court, Dec 8, 2014. Lin, 28, was sentenced to death in February after being convicted of intentionally killing his roommate, Huang Yang, by putting a toxic chemical in their water dispenser. Shanghai-based Xinmin Evening News posted this photo on Sina Weibo. [Photo/weibo.com]

The second trial of Lin Senhao, a former university student who killed his roommate by poisoning, started in Shanghai on Monday morning.

Lin, 28, was a postgraduate student at Fudan University's School of Medicine in Shanghai. In February, he was sentenced to death after being convicted of intentionally killing his roommate, Huang Yang, by putting a toxic chemical in their water dispenser.

The second trial started at 10 am at Shanghai High People's Court, and Lin handed over his 350-word petition for appeal, in which he said he did not intend to kill Huang.

At his first trial, Lin admitted to having spiked the water in the dispenser at their dormitory on March 31, 2013. Huang became sick after drinking the water on April 1, was hospitalized and died of organ failure 15 days later.

At court during the second trial, Lin said he diluted the liquid in the dispenser after he added the toxic chemical, and he questioned how much of toxic chemical Huang ingested or whether that volume could lead to his death.

Lin denied intending to kill Huang, insisting his action was just a prank for April Fools' Day. He said he hadn't thought about the consequences of what he did and just wanted to see how Huang would respond to the prank.

He said he didn't realize the gravity of the situation until April 2, when he heard from classmates that Huang had been taken to hospital. On the night of April 3, he encountered Huang's father and, in spite regretting what he had done, Lin didn't dare tell the truth.

Lin added that he and Huang experienced no enmity and never quarreled or fought with each other. Both had received scholarships, Lin said, and he was not jealous of Huang.

During the first round of questioning at the court, Lin tried to control his feelings several times but finally failed to do so, bursting into tears and becoming unable to speak.

Lin wrote a letter to Huang's parents to apologize before the second trial, but his apology was rejected.

Huang Guoqiang, the victim's father, said Lin couldn't be forgiven for three reasons — the large amount of toxic chemical Lin added to the water, that he didn't tell the truth in time so doctors could try to save Huang's life, and that Lin insisted his action was only a prank.

The case has drawn widespread attention online since it became public in April, with netizens divided in their preferred verdicts. Some insisted on the principle of an eye for an eye, while others said the tragedy had already ended bitterly for one family and there is no need to ruin two brilliant young men and the happiness of two families.