PHOENIX (AP) — An Arizona middle school principal who failed to alert police of an attack planned by four students on her school told them she was going to contact authorities after she finished investigating the threat, police said Wednesday.

The plot involving High Desert Middle School in Globe was foiled several days before it was to be carried out when the mother of another student called police after learning about the threat.

Principal Lori Rodriguez heard of the plot on March 28 and was conducting an internal investigation to determine if it was credible, said Robert Folker, interim police chief in Globe, a mining town about 75 miles (120 kilometers) east of Phoenix.

"Whenever you have someone who has an elaborate plan to carry out an act like this, law enforcement needs to be notified immediately," Folker said.

Attempts to contact Rodriguez weren't successful.

Folker said his agency will recommend the students be charged with interfering with a school. He also said police will recommend an endangerment charge against Rodriguez, who has resigned.

One girl and three boys involved with the plan were suspended. They range in age between 12 and 14.

Folker said the students had a map showing spots at the school that they wanted to attack. The plan called for guns and homemade bombs to be used, but no explosives have been found and the students aren't believed to have brought guns to school.

"They had the plan all written out, and they discussed it and they were going to put their plan into action," Folker said.

A phone message left for Jerry Jennex, superintendent of the Globe Unified School District, wasn't immediately returned.

"This incident has brought to light the fact that we need to make sure that staff does not become complacent and that all of our safety protocols are updated," Jennex wrote in a note posted Monday on the district's website.

___

Follow Jacques Billeaud at twitter.com/jacquesbilleaud. His work can be found at https://bit.ly/2GGWEPO.