When police arrested a 13-year-old boy in Washington state last week accused of making threats to kill, they found he had “everything ready to go to commit a mass shooting” – including a trove of more than 20 guns in his home.

Dorian Johnson, a witness to the 2014 police shooting death of Black teen Michael Brown, was killed by gunfire in Ferguson, Missouri, authorities said. Johnson’s account of Brown’s death inspired the chant at protests against police brutality nationwide: “Hands up, don’t shoot!”