Police in Allen, a Dallas suburb, went to the home for a welfare check at around 1 a.m. Police said the call came from a family friend who said that one of the sons was suicidal.
"The friend had seen the post that his friend made on Instagram, and that’s what made him call and say that he was concerned for his wellbeing," said Allen Police Sgt. Jon Felty.
The social media post said the son had had depression since 2016 and that he had been cutting himself. The message also mentioned the ease with which his brother bought a gun as well as his sadness with the finale of "The Office."
Felty said: "He thought it should have ended much differently and he was upset..."
Police haven’t released the identities of those who died but said they include two teenage brothers, a sister, their father and mother, and a grandmother. Police say the youngest victim was 19.
The two sons were students at the University of Texas at Austin; the sister had a full scholarship to New York University.
The parents were from Bangladesh, and the grandmother was visiting from their native country.
"The mother-in-law was supposed to go back to Bangladesh next month," said Quamrul Ahsan of the Bangladesh Association of North Texas.
Police believe that the slayings happened sometime Saturday, based on the level of bodily decomposition.
"Two brothers entered into an agreement that they were going to complete suicide and from that it went to where the entire family was taken with them," said Felty.
Ahsan believes similar future incidents can be avoided.
"Get to know your family first. Talk to your kids and your children and see what they're up to," Ahsan said. "Talk to your neighbors so nothing like happens like this anymore."
If you or someone you know is having thoughts of suicide, please contact the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).
The Associated Press contributed to this report.