SINGAPORE - A man who fatally stabbed his 56-year-old mother in the heart and punched his 90-year-old grandmother to death after taking mind-altering drug lysergic acid diethylamide (LSD) will be confined indefinitely.

The High Court on Friday found that Gabriel Lien Goh, 25, had committed the acts in 2019 but acquitted him of two charges of culpable homicide on the basis of his mental incapacity.

Goh was found to be of unsound mind when he killed the two women at about 7.25pm on Oct 27, 2019, at Block 7A Commonwealth Avenue owing to his voluntary consumption of LSD, a potent hallucinogen.

The court heard that Goh put a "tab" of LSD – a small square of paper soaked in the drug – under his tongue for about 30 minutes after lunch that day and experienced sensory changes. He took a second tab 1½ hours later out of a sense of curiosity and a desire to see more vivid psychedelic colours, the court heard.

Goh, then a full-time national serviceman, left the flat and returned holding a knife. 
He stabbed his mother, Madam Lee Soh Mui, after she went into his room to talk to him.

The family’s domestic worker, Ms Admini, saw Goh standing in front of Madam Lee, who was on the floor with a stab wound in her chest and the knife plunged into the right side of her head.

Sensing danger, the Indonesian maid left the flat with Goh’s grandmother, Madam See Keng Keng, to seek help from neighbours.

Mr Christopher Choo, 35, who was in the next-door unit with his mother, Madam Chiam Chew Juat, 61, opened the door.

Before the two women could enter, Goh punched his grandmother in the face, causing her to fall and hit her head on the metal railing along the corridor and her dentures to fall out.

Mr Choo told Goh to calm down, but ended up being punched by Goh in the face.

Ms Admini then took Madam See, who was bleeding, into the neighbours’ flat.

Goh grabbed her wrist but she managed to break free and desperately made phone calls to a friend living in the same block and to Goh’s elder brother.

Mr Choo tried talking to Goh again, but the accused punched him multiple times.

When Madam Chiam shouted at Goh to stop, the accused punched both her and his grandmother before leaving the unit.

Mr Choo told his mother to lock the door and windows, and called the police.

A few passers-by who encountered Goh along the sheltered walkway near the block managed to restrain him after he shouted at them and punched one of them in the face.

Madam Lee and Madam See were pronounced dead at the scene by paramedics.

An autopsy found that Madam Lee died from a stab wound that went through her heart.

The autopsy report concluded that when the knife was plunged into her head, she “no longer had an effective circulation for significant bleeding to occur”.

Madam See was found to have died from head injuries.

The court heard that Goh started taking LSD in December 2018 and had taken the drug on three occasions before the incident. 

He had bought the LSD tabs for about $35 to $50 each in Geylang. 

A report from the Institute of Mental Health found that he had acute hallucinogen intoxication at the time of the killings. 

The report said the consumption of the second tab of LSD led Goh to experience feelings of unreality, distortion of shapes, exaggerated colours, illusions, hallucinations, paranoid delusions, and distortion of spatial order and sense of time.

The report said Goh knew full well the potential side effects of LSD consumption – he had done online research on the drug and had experienced a type of paranoid reaction a few months before the killings.

The report said at the time of assessment in November 2019, the drug effects had worn off and Goh’s mental state was normal, although he had a “sense of acute dysphoria” as he came to terms with what he had done.

Justice Valerie Thean ordered Goh to be kept at the Complex Medical Centre in Changi Prison pending further orders from the law minister.

Under the Criminal Procedure Code, in cases where the accused is acquitted on the basis of mental incapacity, the court must order the person to be kept in safe custody and for the case to be reported to the minister.

The law states that the minister may order that person to be confined in a psychiatric institution, prison, or other suitable place of safe custody at the president's pleasure.

It also provides for regular reviews on the person's mental state before any possible discharge.

In November 2021, Goh was sentenced to 22 months' jail after he pleaded guilty to consuming LSD before killing his mother and grandmother, as well as to one count each of LSD and cannabis possession.