TULSA, Oklahoma - Lab tests on a white powdery substance sent to a Tulsa Jail inmate have proved inconclusive, according to the Tulsa County Sheriff's Office.

The unknown chemical was found June 26 when a detention officer opened an inmate's mail which is standard procedure, according to TCSO Major Shannon Clark. The Tulsa Fire Department's Hazmat unit did initial tests on the substance and determined it wasn't a biological agent.

A law officer transported the substance to an Oklahoma City lab that did further testing.

"The Tulsa County Sheriff's Office has now received information that the compound tested negative for any biological chemicals as well as any chemicals that could be hazardous to humans or the environment," a release from TCSO states.

"However, there has been no conclusive test that has yet to determine what the powdery substance was."

TCSO is continuing to investigate the powder, where the letter came from, and what move the sender had, the release states.