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The reward for information leading to an arrest and conviction in a string of Phoenix freeway shootings now stands at $50,000.

SPECIAL SECTION: Phoenix Freeway Shootings

Arizona Department of Public Safety Director Frank Milstead announced at a news conference Monday that the Silent Witness reward has been raised from $20,000.

He says the additional money is coming from the DPS, the Arizona Highway Patrol, the Fraternal Order of Police, the Maricopa County Attorney's Office, the U.S. Marshals Service and other agencies.

Authorities say 11 vehicles have been struck on Phoenix-area highways since Aug. 29.

Eight were hit by bullets and three by projectiles such as BBs and pellets.

Milstead says about 550 of the nearly 1,000 tips received so far are being investigated.

He says someone out there knows something about the shootings.

Anyone with information about these incidents are encouraged to call the DPS Tip Line at 602-644-5805. Additionally, the number for Silent Witness is (480) WITNESS – 480-948-6377.