Anonymous notes threatening to “blow up” a refugee community center catering mainly to Muslim immigrants were found at the Denver-area building, prompting a hate-crime investigation by the FBI, police said on Friday. The two identical, typewritten notes were left on Thursday in the parking lot and stairwell of the Mango House in the Denver suburb of Aurora, both with the message: “WERE GONNA BLOW UP ALL OF YOU REFUGEES,” according to police spokesman Sergeant Chris Amsler.