According to charging documents, Black allegedly abducted Sierra on June 26, 2012, from her West Jordan home about one block from his own home and beat, raped and strangled her before throwing her into a nearby canal, where she drowned.
Three days later, Black was arrested on suspicion of an unrelated bank robbery.
Investigators saw soot and debris on his clothing and hands that was similar to what was in a field where Sierra's clothes were found. Lab results showed Black's DNA matched DNA found on Sierra's body, prosecutors said.
Last August, Black was charged with molesting the other girl from several years before. The girl, who would have been 11 or 12 years old at the time, attended a sleepover with members of Black's family sometime between 2007 and 2009.
Black, according to court documents, entered the bedroom where the girl was sleeping and touched her breasts, put his hands down her underwear and forced her hands to touch his genitals. The next summer, court documents say, Black lured the same girl to his apartment and again put his hands down her pants.
In letters to The Tribune, Black has maintained his innocence. He said police were looking for someone to pin Sierra Newbold's murder on, and he got caught in the cross hairs of the investigation.
"The true [sic] will come out at the end," he wrote.
On Thursday, the family of Sierra Newbold sat in the courtroom surrounded by more than 20 leather-clad members of B.A.C.A (Bikers Against Child Abuse). The bikers, with name tags like "Teddy Bear," surrounded the family protectively as they left the courtroom.
Nearby, members of the Black family hurried down the stairs. They declined to comment on the case.