The father of a former medical student convicted of fatally poisoning his Fudan University roommate has made a personal appeal to the nation's highest court urging it to reject the death penalty imposed in the case.

Lin Zunyao submitted an 18,000-word petition to the criminal division of the Supreme People's Court on Friday. Several lawyers helped him list dozens of points he believed cast doubt on the appropriateness of the original verdict, Beijing Times reported.

China Daily tried to contact Lin for comment, but phone calls went unanswered on Monday.

Lin Senhao, 29, was sentenced to death in his first trial last year for the murder of his roommate, Huang Yang, who died of liver, kidney and lung failure more than two weeks after falling ill in 2013. Lin was accused of adding a deadly poison to Huang's water dispenser.

A second trial upheld the death sentence, and the high court began a review of the sentence three months ago.

Si Weijiang, an attorney at the second trial, said on Monday that the arguments in the petition were already included in their defense pleadings.

"The petition seems to be the father's last battle to secure any chance that his son will be reprieved from the death penalty," he said.

The case sparked national interest because of Lin's status as a medical student at the high-profile Shanghai university.

Lawyer Xie Tongxiang, who specializes in death penalty cases, accompanied Lin to submit the petition. The father turned to Xie after the high court started to review the death penalty, but the lawyer left the case upon Lin Senhao's request. Xie also was unavailable for comment on Monday.

A main point in the new petition revolved around the analysis of the toxin in Huang's body.

Xie has previously said the court's verdict was based on contradictory test results from two testing institutions. The judicial expertise center under the Shanghai Public Security Bureau found the toxic chemical in the victim's urine, but the Ministry of Justice's Institute of Forensic Science did not.

He also said the chemical was not found in Huang's blood, according to a test report presented by the evidence identification center under the Shanghai bureau.

Some legal experts argued Lin's crime does not make him eligible for a death sentence under the current capital punishment policies. However, they say his father's frequent media appearances might not work in his son's favor.

zhouwenting@chinadaily.com.cn