FORT WORTH, Texas -

Cellphones provided condemning evidence Tuesday against former Fort Worth high school teacher Brittni Colleps, who is on trial for allegedly having sex with five of her students, KENS reports.

Colleps, a 28-year-old mother of three and former English teacher at Kennedale High School, is accused of having group sex with four teenagers while another student videotaped the act with his cellphone, according to The Star Telegram.

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The alleged video was played for members of the jury. The cellphone video did not show Colleps' face, but it reportedly showed a woman's back as she was having intercourse with at least two different students while the others were in the room.

A student pointed out a distinctive tattoo on the teacher's lower back, The Star-Telegram reported.

Colleps was arrested last year when some of the students bragged about the sexual relationship, KENS reported. Some of the students took the stand Tuesday, describing the text messages that prosecutors said were sexual in nature between the students and Colleps.

Colleps is charged with several counts of improper relationship between educator and student. If convicted, she could face up to 20 years in prison.

Although all of the students were over 18 years old, it is against Texas law for a teacher to have an improper relationship with a student, regardless of age. Even if charged and convicted, Colleps would not have to register as a sex offender because all of the students were over the age of 18.