A horrified father heard all three of his children burn to death inside a shed while their mother told him down the phone: "I can hear their screams."
The triple deaths happened in a quiet town close to Brussels in Belgium, after the youngsters were ushered into the shed that was then set alight.
While he was at work on a building site, Helmut Ulin, 38, discovered what was happening when his wife phoned him to reveal what she was doing.
According to local reports, Thioro Mbow told him down the phone: "Listen to their screams."
As Ulin scrambled to reach home from his workplace, which is 12 miles away, Mbow told them: "I can hear their screams but I will do nothing to save them.
"You'd better hurry but you will be too late to rescue them. They won't survive."
Madyson, aged six, Abbygail, four, and Omy, two, all perished in the fire. A fourth child only survived because she was at school when the incident happened.
Witnesses reported Mbow appeared emotionless when the emergency services arrived. The 35-year-old was arrested on suspicion of murder.
A witness told reporters at the scene: "We saw the mother at the scene. There were no tears in her eyes and she did not seem to be in a panic."
The incident reportedly had its roots in a child custody battle between Ulin and Mbow. She recently was sent a letter from his lawyers and did not wish to cede custody of the youngsters.