A brutal murder in Singapore has gone unsolved for nearly 40 years. The murderer has never been brought to justice.

But a YouTube video helped to spark new interest in one of the most terrible crimes ever committed here.

The family

The year is 1979. Tan Kuen Chai and his wife Lee Mei Ying have four children.

• Tan Kok Peng, 10.
• Tan Kok Hin, 8.
• Tan Kok Soon, 6.
• Tan Chin Nee, 5, and the only girl.

The Tan family lived in a one-room apartment at Blk 58, in the Geylang Bahru neighbourhood in Kallang.

The three boys attended Bendemeer Road Primary School, while Chin Nee was still at kindergarten.

Their parents owned a mini-bus, which they operated together to send other children to school. The small business was their main source of income.

The murder

On the morning of Jan. 6, 1979, Tan and Lee left for work at 6.35 am. The four children were at home, sound asleep.

At 7.10 am, Lee called the house to wake the children so they could get ready for school.

No one answered, although she tried calling at least three times.

Worried, she called a neighbour and asked for help to check up on the children. The neighbour went over to knock on the door, but no one answered.

Tan and Lee finally returned home after 10 am, and were greeted by a horrific sight.

All four children had been murdered, slashed to death with their bodies found in the bathroom. The eldest, Kok Peng, had his right arm nearly severed.

According to the pathologist's report, each child suffered a minimum of 20 slash wounds on their bodies.

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The investigation

The investigation was conducted by the Criminal Investigation Department's Special Investigation Section.

The police found that there was no evidence of forced entry, nor was the flat ransacked. No items were reported missing.

However, police believed that a chopper was taken from the kitchen and was used as the murder weapon, along with a dagger. Both weapons were never found.

The investigators concluded that the murders were premeditated and the suspect (or suspects) had taken care not to leave any incriminating evidence behind.

But if the case had occurred in more modern times, things would have been different.

Bloodstains were found in the kitchen sink, as the suspect had apparently cleaned himself off before leaving.

And several hairs were found clutched in Kok Peng's hand -- as if torn off his attacker while he struggled to stay alive.

Unfortunately, DNA testing in 1979 was not as advanced as it is today.

The suspects

Who would possibly want to murder four innocent children?

The police interviewed over 100 of the Tan family's neighbours and made public appeals for witnesses.

Despite several different eyewitness claims, most turned out to be dead-ends.

One neighbour, 68-year-old Yam Yin Tin, usually sat in the common corridor outside her flat, and would have seen anyone going into the Tan residence.

Unfortunately on the day of the murders, she was "washing her hair" and saw nothing.

Another crucial piece of evidence was a card that the Tans received two weeks after the murders.

Disguised as a Chinese New Year greeting, the card depicted happy children playing and had the message "Now you can have no more offspring, ha ha ha."

Written in Mandarin, it was signed off as "The murderer." It also referred to Tan and Lee by their nicknames, "Ah Chai and Ah Eng."

The thing is, Lee had gone for a sterilisation procedure after giving birth to Chin Nee. Only someone close to the family could have known that she was no longer able to have children.

The prime suspect

But it was a lead from one witness that seemed the most promising.

A taxi driver said that on that morning, around 8 am, he picked up a man in his 20s near Block 96 along Kallang Bahru Road, near the scene of the crime.

According to the driver, the man "walked with a lurch", had bloodstains on the "left side" of his body, and carried a knife that "banged against the door" as he alighted at Lavender Street.

From the description, Tan matched it to one of his neighbours, a Malaysian who was close to the family.

He visited the Tan residence almost daily to use their telephone, and was so familiar to the children that they called him "Uncle".

The neighbour was arrested, and during a police line-up, the taxi driver was able to identify him as the same man who boarded his taxi.

But due to a lack of evidence connecting him to the murders, the police released him.

"Uncle" later moved out of Block 58.

The video

On Jan. 12, 2017, YouTuber Cayleigh Elise uploaded a video covering the case.

Elise does a video series on unsolved mysteries like the Tan sibling murders.

She researched Singaporean public records and mystery enthusiasts on Reddit. She also revealed other details, like how Lee later went for a procedure that reversed her sterilisation, and had another baby.

One of the highest rated comments on her video is by a YouTuber called Asotdaze, who claims to know the real story.

He or she claims that the motive for the murders was over an uncollected 4D bet:

"Their parents were supposed to buy some 4D numbers for him. One day his number won, and he wanted to collect his winnings from the Tans, but they said they forgot to buy the numbers that time. He was angry and didn't believe them.

When the Tans bought the mini-school bus to operate their transport business, it confirmed in his mind that they had bought his 4D numbers, but kept his winnings for themselves."

This person claimed that the suspect was involved in gang activities, which made the Tans and their neighbours fear reprisal.

Also, this creepy detail:

"After the murders, there were rumours from the neighbours that they could hear kids running and playing in the Tan apartment at night or when they are not home. Some neighbours also claimed to see ghostly kids running around in the apartment when they looked inside from the kitchen window."

And here are some other comments around the Internet:

Seems compelling, but ultimately, it remains an unverified rumour.

It's unlikely that the murderer of the Tan children will ever be found.

Top image adapted from NewspaperSG.