District Attorney Paul Frasier says it's not known whether Leon Williams Jr., of North Bend, was trying to escape the deputy or committing suicide.
Frasier says a probation officer tried earlier Thursday to arrest Williams on a warrant for escaping supervision of the Oregon Youth Authority. Williams got away, and that officer called the sheriff's office for help.
Frasier says according to the deputy and an eyewitness, the deputy told Williams to stop when he saw him walking across the bridge. Before the deputy could reach him, Williams "vaulted" over the bridge railing.
Williams hit a temporary construction bridge about 90 feet below.
Oregon State Police is leading the investigation.