The sheriff’s office in Fairfax County, Va., released a graphic video on Thursday showing the struggle between officers and a mentally ill woman that preceded her death, and said it was conducting an internal affairs investigation into the episode, in which the officers used a stun gun four times on the woman.

The video was released two days after Commonwealth’s Attorney Raymond F. Morrogh announced that he did not see probable cause to charge the officers with a crime.

“It’s my responsibility as your sheriff to ensure that something like this never happens again,” Sheriff Stacey Kincaid said at the beginning of the video, which is more than 45 minutes long.

Natasha McKenna, 37, who had been given a diagnosis of schizophrenia, bipolar disorder and depression, died in February, days after she was restrained and stunned by officers at the Adult Detention Center. Ms. McKenna was black. The case contributed to an outcry about the treatment of African-Americans by police and raised questions about how the mentally ill are treated in police custody.