A 17-year-old boy's sinister plot to murder his family and then attack his school with pressure- cooker bombs, Molotov cocktails and deadly firearms to kill as many students as he could has been uncovered in the US.

John David LaDue of Waseca, Minnesota, was charged yesterday with four felony counts of first-degree attempted murder, six felony counts of possessing explosive or incendiary devices while under 18 years old and two felony counts of first-degree attempted damage to property.

Police said they found a massive cache of firearms, bomb-making material and at least three completed bombs when they raided LaDue's home. The Bloomington Bomb Squad destroyed the completed bombs at the Waseca Municipal Airport, The Free Press of Mankato reported.

The student is accused of organising an elaborate plot to murder his family and attack his school sometime in the next two weeks in an effort to kill as many students as he could, according to the police complaint.

The boy allegedly laid out all the details of his plot to assault the high school with pressure-cooker bombs, Molotov cocktails and deadly firearms, according to a 180-page notebook obtained from LaDue's bedroom by police.

The notebook outlined LaDue's thoughts about the Columbine, Virginia Tech and Sandy Hook school shootings, police said. He idolised the Columbine shooters, critiquing what they had done right or wrong in their own attack.

LaDue allegedly planned to carry out his school attack on April 20, the anniversary of the Columbine school shooting, but his plan was disrupted by the anniversary falling on Easter Sunday this year.

Police claim that bomb squad officers said it was the largest amount of bomb-making material they had ever seen in their job.

Waseca Police Captain Kris Markeson, during a press conference, said both the high school and the Hartley Elementary School, where remnants of an explosive device were found in March, had been swept and cleared of any bombs.

Markeson said the Waseca police investigation provided no evidence anyone else was involved in LaDue's plot nor any details from his journal noting coordination with other individuals.

Marekson said he believed LaDue would have succeeded with his plot if he had not been discovered before he launched his attack.

Waseca police discovered LaDue when they responded to a call about a suspicious person. The caller said a tall white male with a backpack was observed opening a storage unit, stepping inside and closing the door behind him.