(CNN) Jiranuj Trairat could hear the sudden panic in her cousin's voice.
One minute the cousin was looking at Facebook on his phone, the next he was suddenly shouting Jiranuj's daughter's name: "Beta"
"I was panicked, too, from my cousin's reaction," Jiranuj told CNN over the phone Thursday, audibly distressed. "I grabbed his phone."
As she watched with increasing horror and helplessness, Jiranuj witnessed, live, something no parent should ever have to experience.
"My daughter was sitting with a rope already on her neck," she said. "My husband was tying the rope with something."
Jiranuj immediately dropped the phone and told her cousin to contact the police.
"I knew something very bad was about to happen."
She raced home to try to save her daughter, but she was too late.
Her husband killed their 11-month-old daughter before committing suicide by hanging himself, police on the island of Phuket said. The two bodies were discovered Monday evening, hanging in a derelict building in the Sakhu area of the southern Thai island. Two videos of the murder-suicide were posted on the man's Facebook page.
"How he could do this?" Jiranuj asked.
Police said the man had an abusive history toward his wife. The day before his suicide, he tried to change his wife's Facebook profile picture and they had fought. She was threatened by him, so had left the family home.
Police originally said the act was discovered on Facebook by the father's cousin.
Only on Thursday did it emerge the child's mother had also borne witness to the early stages of the killing.
"I saw that live picture around 5 p.m., and when I arrived it was 6 p.m.," Trairat said. "And it was too late."
Police arrived at the scene at 6:30 p.m., about an hour after the live feed started.
The videos showing the child's death were posted on the man's Facebook page for about 24 hours, Group Capt. Somsak Khaosuwan from Thailand's Ministry of Digital Economy and Society said.
He said the ministry coordinated with Facebook to remove the videos, and they were taken down Tuesday afternoon.
Opinion: Make it a crime to show killing on Facebook
"This is an appalling incident and our hearts go out to the family of the victim. There is absolutely no place for acts of this kind on Facebook," a company spokeswoman said.
Murder raises uncomfortable issues for Facebook, other social networks
Dozens of people, including the girl's mother, attended the baby's funeral Tuesday.