REDWOOD CITY (CBS SF) — A Millbrae middle school teacher pleaded not guilty Monday to having an inappropriate relationship with a 15-year-old former student, San Mateo County District Attorney Steve Wagstaffe said.

Heather Butts, 40, was arrested in August and charged with two counts of lewd acts with a minor in connection with the alleged ongoing relationship with the 15-year-old girl.

An anonymous student tipped off the San Mateo County Sheriff’s Office to the relationship at 5:39 p.m. on Aug. 15, saying that Butts was kissing the student inside a parked van on Santa Helena Avenue near Lomita Park Elementary School, prosecutors said.

Deputies arrived and found Butts alone in the van and the victim nearby. At first the victim denied anything inappropriate had happened, but later admitted that they had been hugging and kissing and said they were in love, according to prosecutors.

A search of the victim’s cellphone turned up a history of explicit text messages, according to prosecutors.

Deputies obtained a warrant for Butts’ arrest and took her into custody at her home the next day.

The girl was a former student of Butts’ at Taylor Middle School and the two had continued seeing each other after the girl started attending Mills High School.

The sheriff’s office admitted shortly after Butts’ arrest that there had been a prior report of inappropriate behavior by Butts last year that wasn’t adequately investigated.

Acting Sheriff Carlos Bolanos released a statement apologizing for the delay in the investigation. An administrative review was opened to look into why it wasn’t handled in a timely manner.

According to Wagstaffe, that report involved contact with the same victim, so he won’t be pursuing any additional charges based on the prior report.

Butts appeared in court in Redwood City Monday to enter the not guilty plea with a retained attorney, Paula Canny. She remains free on $85,000 bail and is scheduled to return to court on Oct. 12 for a preliminary hearing, Wagstaffe said.

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