SALEM (CBS) – The prosecution rested its case Monday in the Colleen Ritzer murder trial after showing the jury more chilling video of the Danvers High School teacher that was recorded shortly before she was killed.

Philip Chism, 16, is charged with raping and murdering Ritzer in a bathroom at the school in October 2013.

Ritzer’s friend and fellow math teacher Sarah Giaquinta took the stand in Essex Superior Court Monday. She watched as prosecutors played surveillance video from a hallway showing Ritzer and Giaquinta having an animated conversation.

She said Ritzer told her she didn’t know why Chism was waiting in her room after class that particular afternoon.

Giaquinta said they were also discussing shampoo and “regular everyday things that we would talk about.”

Sarah Giaquinta on the stand, Nov. 30, 2015. (WBZ-TV)

Sarah Giaquinta on the stand, Nov. 30, 2015. (WBZ-TV)

“She had offered to give me a ride home if I needed one that day and I had told her that I didn’t need one,” Giaquinta said.

In the video, the women were both dressed the same, in black pants and purple shirts, because Giaquinta said it was “dress like your friend day.”

Earlier in the trial, the jury was shown video from the same camera showing Chism, then 14 years old, following Ritzer down the same hallway to the restroom where she was killed.

After Gianquinta left the stand, the jury heard from a pathologist who documented 16 total knife wounds on Ritzer’s neck and head.  She testified that she could not determine a clear cause of death, saying it was either “sharp force injuries” in Ritzer’s neck or asphyxiation.

After the pathologist testified, the prosecution rested.

Earlier Monday, the jury saw video of Chism at two gas stations after Ritzer’s murder.

Philip Chism in Essex Superior Court, Nov. 30, 2015. (WBZ-TV)

Philip Chism in Essex Superior Court, Nov. 30, 2015. (WBZ-TV)

Chism has pleaded not guilty to murder and other charges. His attorney admits Chism killed Ritzer, but claims he isn’t criminally responsible because he is mentally ill.

Comments