Crime report statement baffling

The Oregonian ran this front page article on Sunday relating to an Oregon Criminal Justice Commission Report.

“Experts suggest that Measure 11 has reached the point of diminishing returns. A recent study by the Oregon Criminal Justice Commission, a state agency, concluded that the number of crimes prevented each year by adding one inmate to the Oregon prison system has declined from nearly 30 per new inmate in 1994 to slightly more than 10 crimes in 2005. “

Am I missing something here? It seems like they are saying we ought to let criminals go free earlier because it will only prevent 10 crimes. Isn’t that worth locking someone up, so they don’t victimize 10 more people? 10 may be less than 30, but that number is still horrible. Someone please help me understand that the Commission is not saying what I think they are saying.