More than 120 illegal immigrants with criminal convictions were released back into the United States by federal immigration authorities only to later be charged with "homicide-related" crimes, according to new U.S. Immigration and Customs Enforcement (ICE) data.

"Between FY 2010 and FY 2014, there were 121 unique criminal aliens who had an active case at the time of release and were subsequently charged with homicide-related offenses," ICE Director Sarah Saldaña wrote in a newly released letter to Senate Judiciary Chairman Chuck Grassley, R-Iowa, and Sen. Jeff Flake, R-Ariz.

Thirty-three of those were ordered to be released by immigration courts, while another 24 were released due to the 2001 Zadvydas v. Davis Supreme Court decision, which barred ICE from holding illegal immigrants longer than six months, except in rare cases, such as when an immigrant is ruled mentally ill and dangerous. However, the majority of releases were done at the discretionary request of ICE, meaning officials had the option to keep them in detention, reported the Washington Times.

ICE provided the data in response to a letter from Grassley and Flake, sent following a Jan. 22 incident in which Mexican immigrant Apolinar Altamirano allegedly shot and killed Grant Ronnebeck, a Mesa, Ariz., convenience store clerk, over a pack of cigarettes.

Pending Altamirano's deportation case, ICE initially released him in January 2013 on $10,000 bond, even though he had previously been convicted of burglary charges. While out on bond, Altamirano had two injunctions against harassment issued against him, which is similar to a protection order, reported the Associated Press. Nonetheless, he was allowed to remain out on bond in the U.S.

Because of the aforementioned Supreme Court case, if an alien's home country refuses to take them back, after being detained for six months, ICE is required to release the immigrant into the U.S. while waiting for their deportation proceedings.

Saldaña maintained in her letter that ICE was not aware of Altamirano's criminal injunctions until he was arrested for the convenience store murder.

"There is currently no systematic process for state and local authorities to notify ICE when an injunction or order of protection is served," wrote Saldaña, also admitting that ICE "does not routinely notify local authorities when a detainee is released on bond from ICE custody."

Saldaña said ICE is working to develop new information, sharing protocol through an initiative called the Law Enforcement Notification System (LENS).

Grassley and Sen. Jeff Sessions, R-Ala., sent a follow-up letter Monday to Attorney General Loretta Lynch, Secretary of State John Kerry and Secretary of Homeland Security Jeh Johnson asking how decisions are "made by Justice Department officials to release criminals from custody prior to their deportation." The senators also asked the officials "to explain how they are working together to improve cooperation by other nations with regard to U.S. efforts to deport individuals with criminal convictions."

Since ICE released 2,457 convicted criminal immigrants in 2014 and 1,107, so far, in 2015, the senators, who are seeking a response by July 6, also asked Kerry if he plans to "include a review of visa agreements and foreign aid for nations that habitually refuse to cooperate with the United States' deportation processes."

"Have you considered withholding foreign aid to any of the 12 countries referenced above until the country cooperates on repatriation?" asked the senators. "If so, which countries? If not, why not?"