Tyler Kost, 18, entered the plea through his attorney to 28 felony counts of sexual assault, sexual abuse, sexual conduct with a minor and child molestation for crimes against the girls including one as young as 12 years old.
Kost was ordered held without bond by a judge during a brief hearing in Pinal County Superior Court, said Dwight Fujimoto, the county attorney's chief of staff. His next court date is July 1.
Kost was indicted by a grand jury on May 7 for alleged attacks on 11 girls aged 12 to 17, court documents showed. The alleged attacks date back to 2009. Another charge of sexual conduct with a minor was added in a separate indictment on Wednesday when another girl came forward, Fujimoto said.
The crimes occurred mostly in the victims' bedrooms in San Tan Valley, a town about 50 miles southeast of Phoenix, the indictment said. Kost faces a minimum of 160 years in prison if convicted on all charges, Fujimoto said.
Kost's attorney did not return a telephone call seeking comment.