Hughes, 46, was convicted of the 1988 murders of 15-year-old Shandra Charles and her 3-year-old cousin Marcell Taylor.
At his trial, prosecutors said that Hughes attacked the teen and the child in a field behind an apartment complex in Houston. When found by a passerby, Shandra was still alive, but had been cut on the neck. The boy was already dead. The AP's Michael Graczyk wrote that Shandra "uttered her attacker's first name to police in her dying breaths."
"The fact is I didn't kill anyone," Hughes told Graczyk in an interview last month. (Graczyk took the above photo of Hughes during that interview.)
Hughes used his final words to maintain his innocence, according to the Houston Chronicle's Anita Hassan. "You know I'm innocent, and I love you both," he told his mother and sister, in the observation room. "Please continue to fight for my innocence even though I'm gone."
Hassan described how Hughes' mother wailed as the pentobarbital flowed into his blood stream.
"Oh Preston I love you so much," Johnson shouted. She also made proclamations of her son's innocence.
Hughes could be seen taking a few short breaths before his body lay still.
"Oh God, why?" Johnson cried. "I haven't touched my child in 23 years."
He was pronounced dead 15 minutes later. No other executions are scheduled for 2012.