Flores, of San Gabriel, Calif., was last seen alive with Rivera in Layton on May 9, 2011, according to a probable cause affidavit filed in court.
A family friend told The Salt Lake Tribune in 2011 that Flores left California for Utah on May 7, 2011, with Rivera, who reportedly had promised Flores a construction job.
After Flores disappeared, a missing person report was filed.
But there was no sign of the man until February 2012, when police received a tip directing then to a home at 3812 W. 4550 South, in Roy.
On Feb. 9, 2012, after three days of digging, police found Flores' body under 6-7 feet of earth in the backyard of the home. Police said he had been stabbed to death.
After Flores' body was found, the homeowner, Sarah Munn, was charged with obstruction of justice for allegedly lying to police.
According to court documents filed in Munn's case, Rivera received a laceration to his face that required medical treatment and 35 stitches on May 9, 2011. Munn initially told police that Rivera who lived at the Roy home part-time and is the father of three of Munn's children had received the injury during a road rage incident, then later told police that she caused the cut herself.
Two days later, Rivera rented a tractor in his name and dug a hole in Munn's backyard. According to police, Munn told them that the equipment was used to dig a hole for an in-ground trampoline, but was later filled because the hole was the wrong size.
Flores' body was found in the same area where the hole had been dug, according to the probable cause statement.
Last week, Munn pleaded guilty in a separate drug case, and the obstruction of justice charge was dismissed.
Weber County prosecutors would not discuss whether Munn's plea deal was related to charges being filed against Rivera, though her plea agreement states that she agrees to testify in court when called.
Rivera is scheduled for an initial court appearance on Sept. 25.
Rivera, who has prior convictions for drug distribution and escape from custody, is currently residing at the Utah State Prison in Gunnison.
But the Utah Board of Pardons confirmed Tuesday that Rivera was free on parole from March until June of 2011.