That's not what the "Fatality Analysis Reporting System" (which is published by the U.S. Department of Transportation) says.
FARS Web-Based Encyclopedia
According to a column heading entitled "Fatalities Rate per 100 Million Vehicle Miles Traveled" from the above link traffic fatalities in Arizona have decreased during the period 2001 to 2005 from 2.07 to only 2.01 deaths per one million vehicle miles traveled - far from the 26% your post claims.
In fact, traffic fatalities actually
increased in Arizona for the year 2002 - the next year after you say the traffic cameras were installed.
Look at the same chart for the state of Tennessee. Tennessee's traffic fatalities have decreased from 2.23 to 1.89 deaths per one million vehicle miles traveled (for the time period 1994 through 2005 - which is the time period covered by the table).
Traffic fatalities have been decreasing in all states due to improved vehicle safety features - even in areas where no cameras exist. From just briefly looking at the chart all fifty states had decreases in traffic fatalities per one million vehicle miles traveled from 1994 through 2005.
Much of the decrease can be attributed to improved safety features in cars. Increasingly more powerful computers have enabled auto manufacturers to make safer cars. In the year 2005 cars were much more safe than the 1994 models.
No, traffic cameras have not decreased the traffic fatalities in Arizona. Due to people slamming on their brakes causing rear end crashes the traffic cameras have probably made crashes worse.