SHANGHAI, Dec. 9 -- A Chinese medical student has told an appeals court his poisoning of a roommate last year was intended as an "April fool's joke," rather than murder.

Lin Senhao, a former medical student at Shanghai's Fudan University, appealed on Monday against the intentional homicide charge and death penalty handed down at a local court in February.

He was convicted of using N-Nitrosodimethylamine, a deadly chemical compound from the university's lab, to contaminate a water dispenser in the dorm he shared with Huang Yang.

Huang drank from the dispenser on April 1 last year and died of organ failure two weeks later.

Monday's debate, which lasted more than 13 hours at Shanghai Higher People's Court, centered on the immediate cause of the victim's death, as noted coroner Hu Zhiqiang suggested Huang had died of Hepatitis B and subsequent organ failure.

Hu, who was present at the appeals court at the request of Lin's defense attorney, cited clinical records indicating Huang had tested positive for the Hepatitis B antibody, which "could not have been directly related to poisoning," he argued.

The prosecutor, however, disputed Hu's claim, whose assertions derived only from past literature and clinical records, rather than autopsy findings.

At the appeals court, the previously taciturn Lin spoke out. He insisted he had not intended to kill Huang. "It was just a prank for April Fool's Day, and I watered down the chemical," he told the Shanghai Higher People's Court.

The court had evidence that Lin searched for information online about the chemical several times before adding it to the water dispenser on March 31, 2013, including information about its smell and taste, as well as symptoms and poisoning diagnosis.

Lin did not confess to contaminating the water dispenser until he was interrogated by police on April 12.

According to the court verdict handed down in February, the poisoning was motivated by Lin's growing discontent with Huang over trivial matters after Huang moved into the same dorm in August 2011.

"I am rather hollow, with no ethics or value," said the 28-year-old Lin when he was asked to say something to Huang's parents. "If I'm lucky enough to survive (the death penalty), I will do everything I can to compensate you. If not, I hope you will shake off the shadow and carry on."

Huang's father, Huang Guoqiang, from Sichuan Province, insisted Lin deserved the death penalty. But Lin's father, Lin Zunyao from Guangdong Province, feared his son might have been wronged. "I know him well. He's such a good boy. He couldn't have meant to kill."

The court said it will announce the verdict soon.

The public was also divided over whether Lin deserves death. While many demanded "life for a life," some also said Chinese courts should use the death penalty more sparingly and cautiously.

The poisoning made headlines, prompting national outcry and soul-searching on the moral education of Chinese youth. It also brought to the spotlight again the long-forgotten case of Zhu Ling, a chemical major at Beijing's Tsinghua University who suffered severe brain damage after being poisoned with thallium in 1994.

Zhu's roommate was suspected to be responsible, but charges were never pressed and the case remains unsolved.

Huang's case led to discussions surrounding the tragedy of Zhu, forcing Beijing police to deny widespread speculation that her roommate's family used their influence to hinder the investigation.