Specially trained technicians from the FBI, the ATF and Oregon State Police  descended on Medford Wednesday to investigate an explosion that sounded like a thunder clap and blew the windows out of the Jackson County District Attorney's Office.

No one was hurt in the blast, which took place about 4:30 a.m., but the incident has drawn the full attention of law enforcement.

Greg Fowler, special agent in charge of the FBI in Oregon, said the incident  "demands our singular focus."  The FBI's Evidence Response team from Portland was also sent to Medford, officials said, to collect evidence.

The source of the explosion appears to have been a fuse apparently meant to detonate a 7-gallon propane tank to which the fuse was attached.  The propane tank partially detonated, caught fire, emitted a large flame like a "huge blow torch," then burned out, Medford police Lt. Mike Budreau told the Oregonian newspaper. He said the silver-colored tank is larger than one used on an outdoor grill -- more the size more commonly used in recreational vehicles.