MILWAUKIE, Ore. – A Milwaukie High School math teacher charged last week with having sex with an underaged student was arraigned on additional counts Thursday morning.

Multnomah County

Christopher Klitgord, 29, was arraigned on six charges of sex abuse and two counts of tampering with a witness. It amounted to six additional charges after police arrested him at his Portland apartment on March 31.

 More: Milwaukie math teacher arrested for sex abuse

Klitgord allegedly had an ongoing sexual relationship with a 16-year-old Milwaukie High School girl, who told a school resource officer of the affair.

The school resource officer called police, who then set up a recorded phone call between the girl and Klitgord, according to investigators.

In the phone calls, the girl told Klitgord that police were attempting to contact her. He responded by telling her to "deny all of that." He then told her to "erase" any evidence of their relationship she may have had on her phone, including voice mails and text messages, according to detectives.

Klitgord was placed on administrative leave from his job.