The State Coroner has returned an open verdict in the death of Muhammad Ifan Salam, who was found dead in his father's Toa Payoh flat shortly after dawn on April 7 last year.
The four-year-old had learning disabilities and a history of epilepsy.
He was prescribed the drugs Carbamazepine and Lorazepam to manage his condition.
A third drug, Nitrazepam, was also found in the boy's system during the autopsy. Nitrazepam is a drug of the benzodiazepine class that is used to relieve severe anxiety and insomnia.
Pathologist Marian Wang from the Health Sciences Authority noted that a combination of the three drugs could lead to "excessive drowsiness and, in some instances, death".
State Coroner Marvin Bay said he had to return an open verdict because it could not be determined how the Nitrazepam got into Ifan's body.
"The Nitrazepam in Ifan's blood and urine remains an enigma, since Nitrazepam was never prescribed as a medication for him," Mr Bay said.
The court had earlier heard that Ifan lived with his father because his parents were going through divorce proceedings.
Diagnosed with epilepsy when he was three, the boy had been admitted to hospital for his condition some 25 times.
As he had learning disabilities, he attended a special needs school.
He would walk around the flat and often grab things to put into his mouth or eat. He could also open the refrigerator to feed himself.
On April 6, Ifan's father, Mr Salam Mohammed, fed him some ice cream and bread in the evening before giving him his medication.
After his son fell asleep, he went out to meet a friend at about 7.30pm, leaving his son at home alone.
While he was out, Mr Salam got into a scuffle with his friend and spent some time making a police report. He returned home at about 8.50pm to find Ifan still asleep.
A friend later brought food for the two. When the friend left at close to midnight, Ifan, who had woken up, was still active.
As Mr Salam was feeling tired, he gave Ifan an iPad to amuse himself while he went to sleep.
When Mr Salam woke up at about 7am, his son was motionless. The police arrived at the flat to find him lying on a pillow with his teddy bear next to him.
During investigations, a foil packaging containing a powdery substance and a slab of 10 tablets were found in the kitchen dustbin. The powder and tablets were found to contain Nitrazepam.
The investigation officer said bite marks were found on the foil packet.
Responding to the findings, Mr Bay said it was unlikely an adult would bite a foil packet, but noted that no traces of saliva were found on the packet.
Mr Salam denied any knowledge or ownership of the tablets, saying he hardly cleared his kitchen dustbin and did not know when he last threw something into it.
Furthermore, there was an improvised child gate between the living room and kitchen, and Ifan could not have opened the gate himself.
Mr Salam was arrested for drug offences on the evening of April 7 when his urine tested positive for cannabis and benzodiazepine.
His friends who visited the flat said they did not consume or bring such tablets to his home.
Ifan's mother, Madam Rosnani Ismail, who did not live there, said the only medicine she took to the flat were those prescribed for Ifan.
Mr Bay noted that while Ifan had a risk of sudden unexpected death because of his medical condition, the factor of accidentally consuming unintended drugs could not be removed.
He allowed Madam Rosnani to take her son's teddy bear back, which had previously been seized as evidence.
This article was first published on Mar 14, 2015.
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