Law enforcement said the incident happened on the 400 block of Louisiana Avenue in Bacliff.
Castillo's neighbor, Jesus Excontitta, described hearing his cries for help.
"I heard him screaming, screaming, screaming, pleading, crying," Excontitta said. "I can still hear his voice."
Excontitta said he ran outside to find Castillo getting attacked by both of his pit bulls.
"The dog got him by the arm, and he's crying for help, pleading for help," Excontitta said.
Excontitta described jumping into action and getting a butcher knife to try to fight off one of the dogs.
"One swing and boom," Excontitta said. "Hit him across the face, and he stopped completely. I tried doing the same with the other dog."
When that didn't work, Excontitta said he ran back to get a knife, and he started stabbing the second dog. He said it still wouldn't let go.
"I saw the cop. I ran back over here and I waved the cop down," Excontitta said.
GCSO said when deputies arrived, one dog was still latched onto Castillo's arm. They said they shot the dog, which caused it to let go.
Investigators said Castillo was taken to a nearby hospital, where he later died.
"That's somebody we see every day," Excontitta said. "You don't expect this to happen to, you know, somebody real close to you."
Ultimately, Excontitta said he was surprised by the attack because he believed his neighbor took care of the dogs.
Now, he's trying to wrap his head around losing someone he's known for six years.
"It's just a horrible experience," Excontitta said. "I didn't think that was going to be the last time I talked to him."
The sheriff's office said the two dogs were euthanized by animal control on Monday.