Court of Appeal In September 2021, while Teo's appeal was still pending, convicted murderer
Iskandar Rahmat, who was on death row for a 2013 robbery-murder case, tried to apply for himself to participate in Teo's appeal, so as to provide arguments in support of Teo's constitutionality challenge and to favour his own challenge. The application, however, was disapproved since Iskandar's crime was not related to that of Teo, and the rights to making arguments in Teo's appeal should be reserved to Teo and his defence counsel only. Iskandar's complete exhaustion of his avenues of appeal would make the application unmeritorious if allowed by the appellate court, hence the Court of Appeal dismissed it. It is not known if Teo himself knew about it or if he personally would have allowed Iskandar's participation in his appeal. On 13 October 2021, 11 months after his trial, Teo's appeal against his conviction and sentence was heard at the
Court of Appeal of Singapore. Once again,
Eugene Thuraisingam emphasised to the five-judge appellate panel - which included
Chief Justice Sundaresh Menon and four Judges of Appeal
Steven Chong,
Judith Prakash,
Belinda Ang and
Chao Hick Tin - about Teo's defence of diminished responsibility, arguing that Teo had, in the aftermath of the killings, tried multiple times to commit suicide but fruitlessly, despite the evidence that Teo often behaved and functioned normally up till the murders. Thuraisingam also raised a constitutionality argument regarding first-degree murder (or intentional murder) under Section 300(a) of the
Penal Code of Singapore while declining to proceed with the third defence of sudden and grave provocation. Likewise, the prosecution, led by Winston Man, argued against Thuraisingam's case by citing the High Court's findings on Teo's behaviour before, during and after the murders, which did not substantially support Teo's defence of diminished responsibility, since it is not possible for one who was depressed could be able to function in some scenarios while having the inability to function in another. After hearing the appeal, the five-judge Court of Appeal spent five months before deciding to dismiss Teo's appeal and affirming his death sentence on 23 February 2022. Justice
Judith Prakash, who delivered the verdict, stated that the High Court was correct to identify that Teo did not suffer from diminished responsibility based on his post-killing behaviour and attempts to hide traces of his crime. Justice Prakash also laid out that Teo's reported symptoms were not consistent with the testimonies of his co-workers and family members, which meant that Teo did not suffer from major depressive disorder at all, since he did not display a depressed mood for most of the day nearly everyday or other symptoms like significant weight loss, insomnia or hypersomnia. Having accepted the major points of the lower court's judgement, Justice Prakash and her fellow four judges thus disapproved Teo's appeal and further condemned him to hang for Zi Ning's and Cheong's murders.
Clemency petition After the loss of his appeal, Thuraisingam confirmed that his client would appeal to the
President of Singapore for clemency as a final recourse to avoid execution. However, it was revealed in 2025 that Teo's clemency petition was denied by the President.
Legal challenge against Pacc Act In December 2023, Teo was one of the 36 death row inmates who filed a legal motion to challenge the newly enacted Post-Appeal Applications in Capital Cases Act (Pacc Act), which was designed to manage the last-minute appeals made by death row prisoners who exhausted all avenues of appeal. Teo and his fellow plaintiffs argued that the new law was discriminatory against death row inmates and it would stall the last chances of the convicts' access to justice, which may lead to an unfair legal process. However, Justice Hoo Sheau Peng of the High Court dismissed the appeal, citing that the law was implemented in light of the rising number of inmates filing last-minute appeals before their executions and abusing of court processes, and its purpose was to sift out appeals that were made without merit. She also said that the legal rights of the death row prisoners were not violated by the provisions of the Act, since the law was not passed for enforcement yet. A follow-up appeal by the same 36 plaintiffs was dismissed by the Court of Appeal on 27 March 2024.
Legal challenge against LASCO On 9 May 2024, Teo and another 35 death row prisoners appealed to the High Court, arguing that the policy of the Legal Assistance Scheme for Capital Offences (LASCO) was not to assign counsel for death row inmates who filed further legal motions after exhausting their avenues of appeal against capital punishment and conviction, and this infringed the need to uphold fairness of court processes and constitutional rights of the prisoners, as well as breaching their access to justice and right to legal representation. However, 11 days after the appeal was filed, Justice Dedar Singh Gill found there was no reasonable
cause of action and dismissed the motion, as the LASCO was "perfectly entitled to adopt or change its policy regarding its provision of legal aid", and there could have been multiple reasons for LASCO to not assign lawyers for such convicts, such as the need to allocate resources to aid new defendants who were facing trial and appeal and deter possible abuse of court processes. The judge also stated that the lack of representation from LASCO in post-appeal applications did not deprive the accused persons of their right to life or personal liberty, which was especially so since all the plaintiffs in this case were already convicted and sentenced at this stage, and also exhausted their appeals against conviction and/or sentence, and their rights to access to justice were not violated by the lack of free legal representation, given that they still had the entitlement to engage lawyers on their own accord in any post-appeal applications. Aside from this, Justice Gill said while the applicants should not be deterred from filing applications with merit to prevent the
miscarriage of justice, but any motions launched "at an eleventh hour and without merit" should be regarded as a "stopgap" measure to delay the carrying out of the offender's death sentence. On these grounds, Justice Gill rejected the appeal. ==Execution==