Demond Bluntson, 36, already was being held in a Laredo jail when a judge in another county signed a murder warrant accusing him of killing his girlfriend, 28-year-old Brandy Cerny.
Wharton County District Attorney Josh McCown said the charge could be upgraded to capital murder, but the investigation into various aggravating factors was ongoing.
An aggravated assault charge against Bluntson in Laredo also was expected to be upgraded following the death of 6-year-old Jaydin Thompson in a San Antonio hospital.
Jaydin's great-aunt Dianne Cerny said the boy was taken off life support and died Wednesday evening. She has been speaking on behalf of the family since Jaydin and his 1-year-old half brother were shot Tuesday, the same day their mother's body was found 200 miles away hidden in a shack in their hometown.
The younger boy, Davian Bluntson, died in the shooting at the Laredo hotel. Demond Bluntson is charged with capital murder in his death. Bluntson is being held on $2.5 million bond.
Cerny and her sons were last seen in church Sunday in El Campo. Dianne Cerny said Davian loved playing and exploring, and described Jaydin as being just like his mother.
"He always had an arm around someone, especially his mom and little brother, and he was always laughing and smiling and loving life," she said Thursday. She said Jaydin's family had decided to donate the boy's tissue.
Brandy Cerny's father reported her missing Monday morning after she did not show up for work. El Campo police called their counterparts in Laredo the next day to check on a lead that the family had checked into a Laredo Holiday Inn.
Laredo police said they later determined only Bluntson and the boys had checked in. Officers knocked on their room door about midday Tuesday and immediately heard several gunshots.
Police say when they entered the room, they found Bluntson had shot and killed Davian and wounded Jaydin. Their mother's body was found hours later, in a green shack hidden among trees behind a small house and a mobile home, on an El Campo property where Bluntson's father lived.
Brandy Cerny's family described her as a compassionate and hard-working woman who had earned a bachelor's degree in psychology and was pursuing a master's.
"Brandy worked tirelessly as a single mother to give her sons every opportunity this world had to offer," Dianne Cerny said.
Dianne Cerny said her niece had ended her relationship with Bluntson, but there was "hardly a time when you saw Brandy without her precious sons."
"Our hearts are forever broken and we as a family speak out against domestic violence and ask that anyone who feels threatened seek the necessary help to break free," she said. "Brandy was in the process of breaking free."