Sen. John McCain (R-Ariz.) is pressing Homeland Security Secretary Janet Napolitano for details on the recent supervised release of hundreds of illegal immigrants from detention centers.

Many of the illegal immigrants released by the Immigration Customs Enforcement (ICE) last week were placed on monitoring systems in McCain’s home state. As a senior member of the Senate Homeland Security Committee, McCain asked Napolitano to provide him with more information about the mass release.

“Who within the ICE chain of command has the authority to decide to release a particular criminal alien and what is the written policy limiting the officer’s discretion?” McCain asked in his letter to Napolitano released on Friday.

“What plans are in place to ensure illegal aliens are being detained and we do not return to the days of Border Patrol ‘catch and release’? ”

Key Republicans in both chambers, including House Judiciary Committee Chairman Bob Goodlatte (R-Va.) and Senate Homeland Security appropriator Dan Coats (R-Ind.), have vowed to press the administration for more details on the ICE decision.