Investigators say Rojas-Martinez lashed out after walking in on his wife, Erica, with another man.
"I don't want this to happen to anybody. It's awful," said neighbor Jennifer Audifried.
Neighbors stopping by a memorial building outside the couple's home say they are devastated. Investigators say after his wife's male friend ran off, Rojas-Martinez and his spouse got into a heated fight.
"He took two knives out of the kitchen, started stabbing his wife. stabbed her multiple times. Went into the children's room," said Harris County Assistant District Attorney Colleen Barnett.
Eyewitness News has learned the 19-year-old woman suffered stab wounds to her arms, face, and legs. Investigators say Rojas-Martinez stabbed his 22-month-old son in the chest multiple times. They say his 8-month-old daughter died from the injuries she suffered.
"When the officers were finally able to go into the trailer, the wife was lying on top of the small children," said Barnett.
Rojas-Martinez was crying uncontrollably and his knees appeared to buckle as the judge announced he was charged with capital murder. Police say Rojas-Martinez's toddler is in stable condition. His wife's condition is unknown at this time.
Neighbors say they are just praying for the entire family.
"I just think the devil was here and so we have to pray for them," Audifried.
Neighbors tell us they are planning two rosaries for the baby and family in this mobile home park on Monday night.
