The nightmare began to unfold at Adriane Mathews Gray Elementary School near Houston when one of the female teachers shot a video of her bare breasts while surrounded by a bunch of children's books and toys on campus.

Another clip -- filmed by the teacher -- showed her yanking down her pants and removing her panties to expose herself in a bathroom.

What's even nuttier is that the teacher made no attempt to conceal her identity, with her staff ID reportedly on display at one point.

The woman -- whose name has been withheld for the time being -- claimed that her former boyfriend got his hands on the videos and disseminated them after they called it quits. She filed a complaint with the police, alleging that her ex was engaging in revenge porn.

As for her punishment, the teacher reportedly resigned back in February for unrelated reasons, but is now under criminal investigation, though she has not been charged ... at least not yet. The school first learned about her X-rated flicks this past Wednesday.

Around that time, community activist Quanell X held a press conference, bashing the teacher for her tawdry behavior. Check out the vid ... it's worth the watch.

Meanwhile, on Monday, another staffer from the school was found dead -- the victim of a possible homicide.

The body of Laura Smith -- who worked as the school's Early Childhood Special Education Aide -- was discovered inside her home.

On Tuesday -- the day after her body was found -- Smith's husband abruptly quit his job at the Harris County Precinct 4 Constable's Office as the local sheriff's office launched a murder probe.