McCain wants Napolitano to make public this month the criteria used to determine which detainees were released and how many had been convicted of serious crimes.
"Local sources have raised the possibility that some of the detainees had committed serious crimes such as weapons offenses, smuggling, narcotics trafficking, forgery, aggravated assault against police officers and child molestation," McCain wrote. "The American public needs to be confident that... the Department of Homeland Security (DHS), in fact did not release detainees who will be a danger to the public."
McCain's press office did not respond to a request to identify the local sources the senator cited.
McCain also raised questions about whether the budget cuts have prompted Border Patrol agents to quickly release newly detained illegal immigrants. He requested answers by March 18.
Other Senate and House Republican leaders have also called for a review of the releases. Critics argue that the plan allowed thousands of criminals to return to the street without regard to public safety.
Government documents show the Obama administration planned to release roughly 5,000 immigrants by the end of March. The agency's field offices reported more than 2,000 immigrants were released in February before intense criticism led to a temporary shutdown of the plan, according to the documents.
Immigration officials said the immigrants still eventually face deportation and are required to appear for future court hearings. They must also consent to mandatory check-ins, phone calls, tracking devices or home visits. Violators can be detained again or deported.
McCain is working with a handful of Republican senators to overhaul immigration policy. He has said a path to citizenship for the nation's 11 million illegal immigrants must be contingent on better border security.