Police were battling on Thursday morning to find out why a gunman executed three young women and a man in a bloodbath at a Johannesburg home.

A four-month-old baby was the sole survivor of the tragedy.

Detectives are hoping that 35-year-old Paul Johannes Meyer, who is believed to have lived in the house, can help them clear up the mystery.

The family's domestic worker narrowly missed being caught up in Wednesday's quadruple murder in Albertville, a western suburb of Johannesburg.

She had been sent out moments before to buy baby formula for little Ricardo Lamb.

On her return from the shop, the domestic worker heard the baby's loud cries.

She rushed into the house and found Ricardo's mother, Rosanne Lamb, murdered in the passage of the three-bedroom house.

The child was in his pram.

Two colleagues, 21-year-old Cindy Jeffrey and Linda van Rooyen (who was in her early 30s), were found executed in separate bedrooms.

The fourth victim, a 53-year-old man whose identity was not revealed because his next-of-kin had not been informed, was found in a flatlet on the premises.

All had been shot in the head.

Johannesburg police spokesperson Captain Schalk Bornman said police officers, reacting to an emergency telephone call, found the four lying in pools of blood.

A few minutes later, neighbours arrived and took the baby into their care, while the domestic worker contacted the police.

The baby was later taken away by the Johannesburg Family Violence, Child Protection and Sexual Offences Unit until his maternal grandmother, Rose Lamb, fetched him.

Earlier, the baby's paternal grandmother, who refused to give her name, tried to claim him.

She was denied custody because Ricardo's parents were unmarried.

Wednesday's tragedy was the second to befall the Lamb family.

Chrissie van Zyl told The Star that her brother, Rose Lamb's husband Charles, had been shot and killed in a robbery in Sandton six years ago, when she was four months pregnant.

She said Rose Lamb became worried when she heard about the Albertville shooting on the radio and could not contact her daughter.

Van Zyl said: “I was lying on my bed when my niece came and told me there was a shooting in Albertville.

“As she went out, the phone rang - it was my sister-in-law Rose, who asked whether I had heard about a shooting.

“She said she phoned Rosanne on numerous occasions on her cellphone, and it was just ringing.

“I rushed to pick up Rose and dashed to Ackerman Road, where we found out that Rosanne was among the dead,” Van Zyl said.

Bornman said on Thursday morning that issues leading up to the crime were complicated and detectives were not prepared to speculate on a possible motive, but believed Meyer could provide crucial answers.

He had still not been located by Thursday morning.

Anyone with information can call the investigating officer, Detective Captain Frans Kola, of the Johannesburg Serious and Violent Crime Unit, on 082 557 7109 or Detective Inspector Lappies Labuschagne on 083 755 7954.