"I am sorry to David's family. This is only way that I can be forgiven. You got your justice right here," Vasquez said.
Vasquez, 38, had appealed his execution, but a stay was denied and he was put to death at 6:35 p.m.
Vasquez was convicted of killing 12-year-old David Cardenas in Donna, Texas, 18 years ago. Authorities said Vasquez and his cousin met the boy at a party.
On the night of April 18, 1998, "Vasquez struck the victim in the head with a piece of pipe and a shovel," the Department of Criminal Justice said. "The victim's body was buried behind a residence. ... Vasquez took a ring and a necklace from the victim."
When the boy's' body was found, "he was missing one of his arms and part of the other, had no skin on his back, and had a hole in the back of his head," court documents state
Vasquez "admitted to hitting Cardenas in the head with a pipe and cutting his throat," the U.S. 5th Circuit Court of Appeals said. "He also stated that he and an accomplice dragged Cardenas's body to a field for burial."
Vasquez told police in a videotaped interview that he drank the boy's blood, according to The Monitor
newspaper in South Texas.
"The blood was dripping, and (I) got it all over my face, so I don't know. I mean, something just told me drink," Vasquez said, according to a transcript of the statement.
Vasquez said he tried to cut off the boy's head, according to The Monitor. A detective asked Vasquez why.
"The devil was telling me to take it away from, to keep it, keep it, couldn't come off," Vasquez said. "I was just freaking out cause I was hearing that."
The execution is Texas' sixth of the year.