A 10-year-old Washington state boy has been sentenced to 3 to 5 1/2 years in a juvenile detention facility after participating in a foiled plot to harm children at his elementary school, Laura Myers of Reuters reports.

A second boy, age 11, was also charged in the incident and has a court hearing next month.

On February 7 the 10-year-old brought a working .45 caliber Remington 1911 semi-automatic handgun onto the school bus while the 11-year-old brought a knife, according to prosecutors. The boys also had a list of seven classmates they wanted to harm.

A fourth-grade student spotted the knife and reported it to a teacher's aide, according to prosecutor Tim Rasmussen.

The fifth grader told investigators he and his friend had planned to kill a former fifth-grade girlfriend because she was "rude," "always made fun" of him and friends, "really annoying," and that "he hated her," according to court documents.

Police said the boys showed no remorse.

When asked if he knew what he was planning was wrong, the 10-year-old reportedly replied, "Yes, I just want her dead."

Christina NG of ABC News notes that while the boys were waiting to be taken to a juvenile detention center, the older boy allegedly said: "If I find out who told them about our weapons I'm going to kill them ... I don't care, when I get out of jail I'm going to come back and kill them."

The 10-year-old was charged with conspiracy to commit first-degree murder, juvenile firearm possession, and witness tampering in connection. Prosecutors said he pleaded guilty last month to all charges.

The 11-year-old has been charged with conspiracy to commit first-degree murder, possession of a dangerous weapon in the form of a knife at school, and tampering with a witness.

"As to why children do this, I wish I knew. It is very troubling. It's very scary," Rasmussen told reporters. "I don't have an explanation and the explanation that the boys gave for why they had planned to do this is entirely inadequate."

The incident occurred in Colville, Washington, which is located about 215 miles east of Seattle.