On Tuesday, Everett police arrested 18-year-old Joshua Alexander O’Connor after his grandmother turned over plans she found suggesting he intended to carry out a mass shooting at his High School. The Washington student, according to Everett police, was arrested at ACES High School on charges including suspicion of attempted murder.

Teen was allegedly studying past mass shooting incidents

Authorities say that O’Connor’s grandmother discovered a journal belonging to her grandson detailing plans to use a homemade explosive and to shoot students at the high school. A probable cause document submitted by the Snohomish County Prosecuting Attorney’s Office added that the concerned grandmother immediately dialed 911 and showed the responding officers what she had found.

Court documents report that O’Connor’s goal was to create an infamous shooting incident by causing the highest number of deaths he could. He planned to achieve this through the use of explosives, by activating inert grenades and constructing pressure-cooker bombs.

According to a Seattle Times report, O'Connor wrote in his journal that he couldn’t “wait to walk into that class and blow all those (expletives) away.” It also said that the teen was reviewing past mass shooting incidents [VIDEO] and learning from the shooters’ mistakes.

A spokesman for the Mukilteo School District, Andy Muntz, commended O'Connor’s grandmother on coming forward to report the incident, saying that, “it couldn’t have been easy for her to do.” He added that she had potentially saved many lives, including her grandson’s.

Would-be-shooter did more than write about his plans

O’Connor allegedly wrote in the journal, “I’m preparing myself for the school shooting. I can’t wait. My aim has gotten much more accurate…” He added that his choice of location for the horrific incident was decided by “coin toss” between his former school, Kamiak High School, and his current school, ACES High School -- ACES High School reportedly “won."

According to court documents, O’Connor’s grandmother looked inside of his guitar case after reading the journal and found a semi-automatic rifle. [VIDEO] She told officers that she did not know that O’Connor had a rifle.

The report adds that the responding officers then noticed two military-grade grenades in O’Connor’s room, after which they left the premises to get a warrant. A search of O’Connor’s room also revealed that he was involved in the two-person armed robbery of a nearby convenience store Monday, prosecutors allege.

O’Connor reportedly attempted to escape when taken to the South Everett precinct. The court documents state that he managed to get one hand out of the handcuffs and tried to run but fell on a piece of bark. Police authorities say he “mule-kicked” an officer who was chasing him.

However, according to public defender Rachel Forde, the rifle and grenade shells found in O’Connor’s possession fell under a legal domain. Forde also described the content of O’Connor’s journal as “musings and ventings,” adding that it wasn't enough to support a charge of attempted murder. O'Connor's bail was set at $5 million.