After almost four and half hours of deliberations, a Hidalgo County jury found John Allen Rubio of three counts of capital murder.
The Brownsville man is accused of killing and beheading his three children back in March 2003.
He was given the death penalty but a higher court granted him a new trial that is being heard in Hidalgo County.
The trial started two weeks ago but that last witness testified on Friday.
The jury started their deliberations shortly after 11 a.m. Monday.
The jury returned with their verdict shortly after 3:30 p.m. finding Rubio guilty on all counts.
Rubio had no reaction as the jury read their verdict.
Sentencing has already started in the case.
Prosecutors began closing arguments on Monday morning telling jurors Rubio knew what he was doing when he killed the children.
Rubio has raised the "insanity" defense claiming he thought the children were possessed by demons and that he had to kill them.
Prosecutors said that at no time during statements to police did Rubio say he "killed the demons" and instead always called them the children.
Jurors were shown pictures of the children while they were alive.
Prosecutor Chuck Mattingly became emotional when he explained how they were ferociously killed.
Mattingly asked jurors why Rubio didn't kill his brother and police who he also claimed to be possessed like the children.
"He got rid of three children because he thought they were baggage," Mattingly said. "Angela was going to leave him. They didn't have money."
Mattingly said evidence supports a guilty verdict.
Defense attorneys began closing arguments saying "bodies do not lie."
Nat Perez told jurors if Rubio simply wanted kids dead and gone, he could have put his hand over their mouths and suffocated them supporting their claim that Rubio was insane.
Cameron County District Attorney Armando Villalobos got the last word with jurors.
Villalobos said pulled the knife allegedly used in the murders out from evidence envelope to show the jurors.
The district attorney moved the knife up and down and side to side then signaling on his own neck with his hand how heads were severed.
Villalobos reasserted their position tthat Rubio is not insane.
"If you can decide who to be psychotic in front of, that's not insane...that's manipulative...that's John Allen Rubio," Villalobos told jurors.