As Senate Republicans prepare to take on cities that do not comply with federal immigration authorities, the Center for Immigration Studies reveals that the approximately 340 so-called sanctuary cities in the U.S. have been releasing about 1,000 criminal aliens, combined, monthly.

A new Immigration and Customs Enforcement (ICE) report obtained by CIS expert Jessica Vaughan and detailed in her new report reveals that between January 1 to September 30, 2014 sanctuary jurisdictions released 9,295 criminal aliens that ICE was seeking to deport. More than 600 were released more than once.

Of the released criminal aliens, 62 percent had “significant prior criminal histories or other public safety concerns” in their past before their arrest — 58 percent of those criminal aliens with a prior history had prior felony charges or convictions, 37 percent had a serious misdemeanor charge and 5 percent had multiple prior misdemeanors.

According to Vaughan’s report, 2,320 of the criminal aliens released by sanctuary cities were rearrested within the nine month timeframe in which they were released for new crimes. Vaughan highlighted the case of Victor Aureliano Hernandez Ramirez who allegedly raped and killed a 64-year-old woman after the Santa Barbara County Sheriff ignored a detainer on ICE placed on him following an earlier battery arrest.

The majority of criminal aliens released by sanctuary cities in the timeframe studied have remained on the streets. The CIS report reveals that as of last year 69 percent were still at large, and of those still on the streets about 20 percent were arrested again.

“Our elected officials must not continue to sit back and watch these sanctuary jurisdictions release thousands and thousands of deportable criminal aliens back into our communities in defiance of ICE efforts to deport them, and then witness the harm that inevitably ensues when these removable offenders strike again,” Vaughan said Thursday.

“There is no more obvious immigration issue on which Congress could act now than to rein in this obstruction of a vital law enforcement mission that keeps our communities safer,” she added.

The issue of sanctuary cities became front page news in July with the murder of Kathryn Steinle, allegedly by a multiple deportee illegal immigrant with a long rap sheet. Local authorities in the sanctuary city of San Francisco had released the shooter — despite an ICE detainer — mere months before he killed Steinle.

In reaction to Steinle’s murder the House passed a bill to restrict federal funding to jurisdictions that refuse to comply with federal immigration requests. This month the Senate is slated to vote on legislation introduced by Sen. David Vitter (R-LA) called the “Stop Sanctuary Policies and Protect Americans Act” that also targets sanctuary cities and offers legal protections to local law enforcement that cooperates with federal immigration authorities.

CIS complied a list of sanctuary jurisdictions in July revealing that the federal government had identified 276 such areas as of September 2014. Thursday, CIS reported that ICE updated its list in December, bringing the total number of jurisdiction up to 340.