How do ICE detainers and Warrant Service Officer agreements affect custodial arrest counts?
Executive summary
ICE detainers—civil requests that jails hold people for immigration authorities—and Warrant Service Officer (WSO) agreements—contracts that deputize state or local officers to execute ICE warrants—both change where and when custody is counted, and therefore can materially inflate or redistribute custodial arrest figures reported by and about ICE [1] [2]. Disputes between federal and state figures illustrate how counting rules, transfers, and informal practices make it difficult to map a single “true” custodial arrest total [3] [4].
1. How detainers operate and why they complicate custodial counts
An ICE detainer is a nonjudicial request asking a jail or prison to hold someone beyond their scheduled release time so ICE can decide whether to take custody; ICE’s own materials describe detainers as a mechanism to secure presence for immigration proceedings and to facilitate transfers from CBP and other agencies into ICE custody [1] [5]. Because detainers rely on local facilities to extend custody, counting who was “arrested by ICE” can vary: ICE may count a person as an ICE arrest if the agency subsequently takes custody after a detainer, while a state may report it never honored the detainer or that the individual was released without an ICE transfer—creating conflicting tallies [3]. Historical FOIA data and third‑party archives show ICE records include linked identifiers across arrests and detainers that can be merged, but datasets are incomplete enough that tracing an individual’s pathway through local custody, detainer holds, and ICE arrest is often nontrivial [2].
2. Warrant Service Officer agreements and the expansion of interior arrests
WSO agreements deputize state or local officers to serve ICE civil warrants and can shift arrests out of traditional ICE tactical operations into routine policing encounters, which changes when and by whom custodial events are recorded [2]. When local officers execute ICE warrants under WSO programs, those arrests may appear in local arrest logs rather than as headline ICE raids, yet ICE’s aggregated arrest and detention statistics will still reflect those transfers—blurring lines between “ICE arrests” and local-law enforcement arrests and making direct comparisons of custodial counts across jurisdictions misleading without careful data linkage [2] [6].
3. How counting conventions and timing alter reported detention growth
Different counting conventions—“midnight population” versus 24‑hour counts—produce divergent snapshots of custody levels, and rapid transfer practices (from CBP to ICE, from jails to ICE custody) mean a person can be booked several times in different systems on the same day, multiplying entries in administrative datasets [4] [1]. Independent trackers and advocacy analyses show dramatic rises in ICE custody that are concentrated among people with no criminal convictions, a trend partly explained by increases in interior arrests and transfers rather than only border apprehensions; but these same analyses warn that arrest-versus-custody definitions matter when interpreting growth rates [7] [8] [9].
4. Evidence of mismatches and the politics of the counts
Concrete disputes underscore the stakes: Minnesota officials reported roughly 300 people in custody with ICE detainers in a state survey, while DHS publicly cited 1,360 pending detainers—an explicit example of how federal and state figures can diverge and how detainer lists do not always translate into custodial transfers or ICE arrests as the federal government describes [3]. Advocates and watchdogs argue that policy choices—WSO programs, aggressive interior arrest directives, and quotas—produce more at‑large arrests and court‑appearance re‑arrests, altering the composition of the detained population and expanding counts of people “booked into detention” [6] [10].
5. What can and cannot be concluded from the public record
Public records and independent datasets confirm that detention growth has been real and that transfers and interior enforcement strategies strongly affect who shows up in ICE custody—especially the increase in detainees without criminal convictions—yet available data and counting rules limit the ability to state definitively how many custodial arrests are purely ICE-initiated versus the product of detainers or WSO-facilitated local arrests without careful record linkage [7] [11] [2]. ICE’s own explanations emphasize transfer and custody decisions by multiple actors (CBP, jails, ICE, immigration judges), which means custody statistics should be read as the outcome of administrative cooperation and timing, not a single type of arrest event [1] [5].