Immigration Bond, Federal Immigration Bail Bonds, Delivery Bond, Voluntary Departure Bond

The numbers, which were generated by the County Attorney''s Office, reinforce popular beliefs about illegal immigration and crime but contradict the findings of some sociologists and journalists.

The Republic reported earlier this year, for example, that only 10 percent of bookings into Maricopa County jails in the last six months of 2007 were subject to holds by the federal Immigration and Customs Enforcement Agency. That percentage was based on numbers provided by the Maricopa County Sheriff''s Office - numbers that the office later tried to refute. 

Similarly, a study released last week that was conducted by researchers at Arizona State University on behalf of the Maricopa County Board of Supervisors indicated that only 10 percent of the county jail inmate population in 2007 were undocumented immigrants, 2 percent were legal immigrants and 88 percent were U.S. citizens.

But the study released by Thomas on Thursday, which focuses on persons who are actually convicted, says that 18.7 percent of convicted felons in Maricopa County last year were undocumented immigrants.

In the past, Thomas'' office has balked at providing numbers of illegal immigrants prosecuted for crimes other than those related to the state''s human-smuggling statutes, and the county attorney denied that the release of the study was politically timed.

Thomas faces Democrat Tim Nelson and Libertarian Michael Kielsky in the Nov. 4 election.

"I understand there is great passion related to the illegal-immigration debate," Thomas said. "And I am not trying to incite anything or pour gasoline on the flames, but the public has a legitimate right to know whether there is a link between crime and illegal immigration."

It has been a difficult link to quantify because law-enforcement agencies have been loath to document such trends.

Until the passage of Proposition 100, the law that denies bond to illegal immigrants accused of serious crimes and until sheriff''s deputies became certified to conduct investigations into citizenship, it was nearly impossible to do so.

According to Thomas'' findings, in 2007, illegal immigrants accounted for:

• 12.8 percent of aggravated-assault convictions.

• 33.5 percent of drug convictions.

• 35.8 percent of kidnappings.

• 13 percent of robberies.

• 20.3 percent of felony DUIs.

• 20.7 percent of crimes with weapons.

• 10.6 percent of murders and manslaughters.

The percentages were higher for crimes generally associated with illegal immigrants, such as:

• 96 percent of smuggling cases.

• 44.4 percent of forgeries and frauds.

• 85.3 percent of false-ID convictions.