Authorities say last week’s blast that killed two Cedar Rapids-area boys and critically-injured a third was caused by a homemade bomb. The Linn County Sheriff has concluded the investigation into the August 17th explosion in rural Palo. The blast was caused by the accidental detonation of “an improvised explosive device.” 18-year-olds Tyler Buelow of rural Palo and Grant Rutherford of Cedar Rapids died in the blast, while Ryan Rezin, of Cedar Rapids, remains in critical condition at University Hospitals in Iowa City.