Prosecutors say Jonathan James was deprived of water for days as punishment for bedwetting and other indiscretions during record high temperatures in July 2011. Stepmother Tina Maria Alberson is charged in the boy's dehydration death.
The boy's fraternal twin Joseph, now 12, testified Thursday, saying he thought his brother was suffering but he was too afraid of his stepmother to do anything.
"He would be asking for water and she would say, 'No, because you're in trouble,'" the boy said in court, adding, in reference to his dead brother, "We were very close. We loved each other."
The boys' father, Michael Ray James, testified against her Wednesday "to see that justice gets done in the interest of my son," he said.
The father will be tried next month on the same charge, The Dallas Morning News reported Thursday.