A woman prevented a potential tragedy this week when she reported her 18-year-old grandson to police after learning of his plot to carry out a mass shooting at his high school.

Everett police in Washington state arrested 18-year-old Joshua Alexander O'Connor at ACES High School on Tuesday, on suspicion of attempted murder. The arrest was made after O'Connor's grandmother called 911 and turned in a notebook where he had detailed plans to use homemade explosives and shoot students at his school.

"I need to make this count," O’Connor reportedly wrote in the journal. "I’ve been reviewing many mass shootings/bombings (and attempted bombings) I’m learning from past shooters/bombers mistakes."

O'Connor also reportedly noted that he wanted the death count to be high so he would be infamous. Court papers also detail that his discovered notebook included instructions about making pressure-cooker bombs and grenades.

"We are really grateful to the grandmother. It couldn’t have been easy for her to do," Mukilteo School District spokesman Andy Muntz said. "It speaks to the importance of the saying, 'if you hear something or see something, call authorities,' and that’s what she did. It's quite possible she saved many lives including her grandson's."

According to Snohomish County Jail records, O'Connor's bail has been set at $5 million.

RELATED: The 25 fatal school shootings since Columbine



25 PHOTOS 25 fatal school shootings since Columbine See Gallery 25 fatal school shootings since Columbine April 20, 1999 - Columbine High School Photo Credit: Reuters Nov. 20, 1999 - Deming Middle School, New Mexico (photo by Joe Raedle) February 29, 2000 - Buell Elementary School, Michigan Photo Credit: Reuters May 26, 2000 - Lake Worth Middle School, Florida Photo Credit: Reuters March 5, 2001 - Santana High School, California Photo Credit: REUTERS/Mike Blake MB/RCS April 25, 2003 - Red Lion Area Junior High School, Pennsylvania Photo Credit: Reuters September 24, 2003 - Rocori High School, Minnesota Photo Credit: Getty March 21, 2005. Red Lake High School, Minnesota REUTERS/John Gress November 8, 2005 - Campbell County Comprehensive High School, Tennessee Photo Credit: Getty Aug. 24, 2006 - Essex Elementary School, Vermont Photo Credit: Getty September 29, 2006 - Weston High School, Wisconsin (Photo by Darren Hauck/Getty Images) October 2, 2006 - West Nickel Mines School, Pennsylvania (Photo credit should read STAN HONDA/AFP/Getty Images) January 5, 2011 - Millard South High School, Nebraska Photo Credit: Getty February 27, 2012 - Chardon High School, Ohio REUTERS/Aaron Josefczyk December 14, 2012 - Sandy Hook Elementary, Connecticut (Photo by Mario Tama/Getty Images) October 21, 2013 - Sparks Middle School, Nevada. (Photo by David Calvert/Getty Images) December 13, 2013 - Arapahoe High School, Colorado REUTERS/Rick Wilking June 10, 2014 - Reynolds High School, Oregon (Photo by Natalie Behring/Getty Images) October 24, 2014 - Marysville-Pilchuck High School, Washington REUTERS/Jason February 12, 2016 - Independence High School, Arizona Photo Credit: Getty September 28, 2016 - Townville Elementary, South Carolina (Photo by Ricky Carioti/The Washington Post via Getty Images) April 10, 2017 - North Park Elementary School, California (Photo by David McNew/Getty Images) September 13, 2017 - Freeman High School, Washington Photo Credit: Getty January 23, 2018 - Marshall County High School, Kentucky REUTERS/Harrison McClary February 14, 2018 - Marjory Stoneman Douglas High School, Florida (Photo by Joe Raedle/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

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