(CNN)Brent Oxley, an Immigration and Customs Enforcement deportation officer in Little Rock, Arkansas, was happy in his work, which he says "gave me the feeling that I was helping protect my country." A big part of his job: Look through rosters from local jails for people who might be deportable, ask for them to be held for ICE to pick up, then go get them.
ICE supervisors sometimes skip required review of detention warrants, emails show
But last May, ICE fired Oxley, for a variety of charges that included forging his supervisor's signature on arrest warrants for undocumented immigrants. Federal immigration law requires each warrant to be signed by an authorized supervisor. By signing them himself, an ICE administrator wrote to Oxley, he had exposed ICE to the possibility of "numerous unlawful detention lawsuits" over illegal arrests, had they not reissued the warrants.
Oxley challenged his termination, convinced he had not been alone in skipping the warrant-review process, which could be inconvenient when supervisors weren't in the office and the 48-hour time limit to release people was nearing its end. And he turned up evidence he was right.
Internal emails and other ICE documents he obtained through a Freedom of Information Act request, since reviewed by CNN, show that other officers across the five-state region where Oxley worked had improperly signed warrants on behalf of their supervisors -- especially on evenings or weekends. Some supervisors even gave their officers pre-signed blank warrants — in effect, illegally handing them the authority to begin the deportation process.
Unlike Oxley, who outright forged his supervisor's signature, the other officers generally signed for their supervisors after getting their permission via text or phone. But in such cases -- or when officers were given blank, pre-signed warrants -- it's unclear how closely or even whether a supervisor would have reviewed an individual case.
Legally, the signature on a warrant attests that an authorized supervisor reviewed it and determined that there was probable cause to believe the person named was deportable. The Immigration and Naturalization Act doesn't offer the option of letting unauthorized officers sign for supervisors.
Two other ICE employees told CNN that they're aware of similar incidents of supervisors elsewhere in the country providing pre-signed blank warrants or telling officers to sign for them without full review, and that the practice is ongoing.
Lawyers and advocates interviewed by CNN expressed surprise about the improperly signed warrants, which could be used to challenge individual deportation orders at immigration hearings.
"If there's evidence of that, that's a big deal," said Jeremy McKinney, a member of the executive committee of the American Immigration Lawyers Association, whose members represent clients in deportations and immigration matters. "That's the root of an illegal arrest."
More broadly, improperly signed warrants could become a point of contention in several ongoing lawsuits over ICE's practice of asking law enforcement to hold undocumented immigrants in detention up to 48 hours longer than they otherwise would. With each such request, called a detainer, ICE sends along a warrant.
"This is very relevant to those cases," said Lena Graber, staff attorney at the Immigrant Legal Resource Center, in San Francisco. "When we think about what a warrant is, it's based on preapproval from a neutral party determining that there are facts supporting an arrest. When there isn't even an administrative review, that's pretty egregious."
ICE's practice of asking law enforcement to hold immigrants -- some being released from jail or prison, some picked up by sheriffs or police without ever being charged with a crime -- has long been a source of concern for civil rights groups and city governments. Many jurisdictions have refused to comply with the requests, and immigrant-rights groups have sued the agency over the practice multiple times.
Two years ago, in an attempt to address those concerns and to conform with court rulings, ICE implemented a new rule that required that every detainer be accompanied by a warrant, and that authorized supervisors review and sign the warrants.