Flowers and eight balloons left at a house where eight people were killed (AP)

A woman who previously dated the man accused of fatally shooting her, her husband and six children had texted her mother before her death that she was being held at gunpoint.

Harris County district attorney Devon Anderson said after the man appeared in court that authorities had been alerted of problems at the Houston, Texas, home by the mother of victim Valerie Jackson.

"My heart goes out to the mother who received the text from her daughter that she was in trouble, and the mother was many states away but of course did what any mother would do and called 911," Ms Anderson said.

David Conley, 48, who has been charged with capital murder, stood handcuffed and shackled before state district judge Vanessa Velasquez as the probable cause warrant naming him was read.

There was no mention of a lawyer either appointed or hired during the court hearing. His only response was to acknowledge his name when asked by the judge, who also read him his rights.

Those killed, who all were shot in the head, were identified as parents Dewayne Jackson, 50; his wife, Valerie Jackson, 40; and their children Dewayne, 10; Honesty, 11; Caleb, nine; Trinity, seven; and Jonah, six. Also killed was a 13-year-old, Nathaniel, who was believed to be Conley's son from the relationship with Valerie Jackson.

Most of the victims had been handcuffed and some had been shot multiple times, police have said.

"We do not - cannot - fully comprehend the motivation of an individual that would take the lives of so many innocent people. Especially the lives of the young ones," said chief deputy Tim Cannon of the Harris County Sheriff's Office. "The killer's motives appear to be related to a dispute with Valerie, who was his former domestic partner."

Ms Anderson said it would be three to four months before she decides whether to seek the death penalty.

The request from Valerie Jackson's mother on Saturday sent officres to the home in north-west Houston.

"Upon arrival, deputies made multiple attempts to establish contact with residents inside the home. No contact was made," Mr Cannon said.

After authorities learned that Conley, who had once lived in the home, had a warrant for his arrest for an assault charge, the sheriff's office High Risk Operations Unit was called.

"While awaiting response for the (unit), the body of an unidentified child was observed through a window at the residence," he said. "Deputies on scene forced entry into the home and were immediately met with gunfire. The deputies withdrew from the home ... and awaited the arrival of the" unit.

A stand-off ensued for several hours until Conley surrendered, said Sergeant Craig Clopton, the lead investigator.

Investigators declined to say when on Saturday the victims were shot or if any victims were alive when deputies first tried to enter the home.

According to an arrest affidavit, Conley told authorities that he discovered on Saturday morning that the locks had been changed at the home after he had moved out. He entered the home through an unlocked window, the affidavit said.

According to Sgt Clopton, Valerie Jackson and Conley had a relationship, which ended, and "then (Dewayne Jackson) began a relationship with Valerie, which led to five children".

That relationship ended and Conley and Valerie Jackson began another relationship, before breaking up again, Sgt Clopton said.

Court records show Conley's criminal history dates back to at least 1988, with the most recent incident last month, when he was charged with assault after allegedly assaulting Valerie Jackson at the home where the bodies were found.

PA Media