A 19-year-old Portola Valley man arrested on suspicion of sexually assaulting a minor has pleaded not guilty, according to the San Mateo County District Attorney's Office.

James Nell Jr. was arrested Thursday, Sept. 24, in San Mateo on suspicion of lewd acts with a child under 14 years old, oral copulation with a child under 14 years old, sexual intercourse with a minor and furnishing harmful matter to a minor, according to the San Mateo County Sheriff's Office.

Nell Jr. and the victim, a 13-year-old girl, started talking through social media, according to District Attorney Steve Wagstaffe. Nell Jr. then sent her a sexually explicit video over Snapchat and said his friend would pay her for nude photos, Wagstaffe said.

The victim ran away from home, and Nell Jr. brought her to his Portola Valley home where he sexually assaulted her, according to the DA's office. Nell Jr. then warned the girl not to tell anyone or they would get in trouble, adding he would kill himself if he went to jail, Wagstaffe said.

The girl later returned home, and Nell Jr. visited and sexually assaulted her there as well, according to the DA's office. The victim's mother learned about the incidents upon reviewing text messages on her daughter's cellphone.

In August, Sheriff's Office detectives began investigating a report of a sexual assault case involving a minor under the age of 14 that occurred on July 1. The incidents took place between May 1 and July 1, prosecutors said.

Nell Jr. appeared at a felony arraignment hearing on Monday, where he pleaded not guilty and was appointed a private defender. A preliminary hearing has been scheduled for 2 p.m. on Oct. 7.

Nell Jr. remains in custody with bail set at $200,000. The court granted prosecutors' request for an order barring him from contacting the victim.