By Daniel Kugler1

The Fourth Amend­ment pro­vides that war­rants must be sup­port­ed by prob­a­ble cause and “par­tic­u­lar­ly [describe] the place to be searched, and the per­sons or things to be seized.”2 Deter­min­ing whether prob­a­ble cause exists is both a neb­u­lous fact-inten­sive inquiry under the “total­i­ty of the cir­cum­stances” analy­sis and a cru­cial safe­guard against uncon­sti­tu­tion­al search­es.3 Courts con­sis­tent­ly con­front and must apply this analy­sis to new and unset­tled fac­tu­al cir­cum­stances. It remains unde­cid­ed whether prob­a­ble cause to issue a search war­rant for evi­dence of ter­ror­ism exists where the mag­is­trate is only pre­sent­ed with a tip­ster who alleges their ex-spouse is a ter­ror­ist and the accused’s unre­lat­ed crim­i­nal records. Although fact-spe­cif­ic, as prob­a­ble cause analy­ses must be, the issues addressed in this Con­tri­bu­tion have sig­nif­i­cant ram­i­fi­ca­tions giv­en the grav­i­ty of alleg­ing ter­ror­ism and the mass num­ber of Amer­i­cans with crim­i­nal records.

This Con­tri­bu­tion will argue that a war­rant based on a citizen’s unre­lat­ed crim­i­nal records and their for­mer spouse’s gen­er­al­ized alle­ga­tions of ter­ror­ism lacks prob­a­ble cause.

* * * * *

A mag­is­trate deter­mines prob­a­ble cause by weigh­ing the “total­i­ty of the cir­cum­stances,” which include the “verac­i­ty,” “basis of knowl­edge,” and oth­er “indi­cia of reli­a­bil­i­ty” of per­sons sup­ply­ing infor­ma­tion for the search war­rant affi­davit.4 Although each of these fac­tors need not be present and strength in one fac­tor may com­pen­sate for weak­ness in anoth­er, the absence of either verac­i­ty or basis of knowl­edge weighs against find­ing prob­a­ble cause.5 This frame­work, estab­lished by the Supreme Court in Illi­nois v. Gates, replaced the pri­or two-prong test with a “prac­ti­cal, com­mon-sense approach” involv­ing these “inter­twined” ele­ments.6 Courts’ analy­sis of these elements—veracity, basis of knowl­edge, and alter­na­tive indi­cia of reliability—provides guid­ance for assess­ing tips of ter­ror­ism and the rel­e­vance of the accused’s crim­i­nal past.

Verac­i­ty is strongest when the tip includes police cor­rob­o­ra­tion and pre­dic­tive infor­ma­tion sus­cep­ti­ble to corroboration—e.g. the accused will com­mit X crime on Y street at Z future time.7ver­i­fi­ca­tion of those alleged posts is an effi­cient and effec­tive method for strength­en­ing the verac­i­ty of the tip. Law enforce­ment can typ­i­cal­ly access social media accounts, includ­ing Twit­ter, because they are vis­i­ble to the “pub­lic by default”8 and even where social media accounts are set to “pri­vate” and only vis­i­ble to “friends” or “fol­low­ers,” law enforce­ment can view and ver­i­fy alleged posts with the assis­tance of the tip­ster or use of a con­fi­den­tial infor­mant.9

A basis of knowl­edge is estab­lished by detailed infor­ma­tion based on an informant’s per­son­al and recent obser­va­tions. Even an informant’s for­mer mar­i­tal rela­tion­ship to the accused, how­ev­er, is insuf­fi­cient alone to estab­lish a suf­fi­cient basis of knowl­edge.10 In Unit­ed States v. Fly­nn, the Fifth Cir­cuit explained that infor­mants with an inti­mate con­nec­tion to the accused “may have per­son­al rea­sons for giv­ing shad­ed or oth­er­wise inac­cu­rate infor­ma­tion to law enforce­ment offi­cials,” and there­fore it is inap­pro­pri­ate to pre­sume a basis of knowl­edge based on that rela­tion­ship.11

Where there is nei­ther strong verac­i­ty in the alle­ga­tions made nor a strong show­ing of basis of knowl­edge, no prob­a­ble cause exists under the total­i­ty of the cir­cum­stances absent oth­er indi­cia of reli­a­bil­i­ty capa­ble of over­com­ing these defi­cien­cies.12 Law enforce­ment may con­tend that both an accused’s pri­or crim­i­nal record and the nature of ter­ror­ism alle­ga­tions should con­sti­tute such alter­na­tive indi­cia of reliability.

Although an issue of first impres­sion, exist­ing Fourth Amend­ment jurispru­dence sug­gests that an accused’s crim­i­nal record—including pri­or con­vic­tions and out­stand­ing arrest warrants—unrelated to the offense named in the war­rant appli­ca­tion does not estab­lish a strong indi­ci­um of reli­a­bil­i­ty or prob­a­ble cause. In Brine­gar v. Unit­ed States, the Supreme Court held that an officer’s knowl­edge that he had arrest­ed the same defen­dant months ear­li­er for the same crime sus­pect­ed, and that the defen­dant had been indict­ed for it, prop­er­ly con­tributed to find­ing prob­a­ble cause to search the defen­dant for con­tra­band of that crime.13 The Ninth Cir­cuit inter­pret­ed this to mean that a defendant’s crim­i­nal his­to­ry may be rel­e­vant to the prob­a­ble cause cal­cu­lus, but it cau­tioned, con­sis­tent with oth­er cir­cuits, that crim­i­nal his­to­ry “can­not alone estab­lish rea­son­able sus­pi­cion or prob­a­ble cause.”14

The extent to which the grave nature of ter­ror­ism alle­ga­tions con­sti­tutes a strong indi­ci­um of reli­a­bil­i­ty also remains unset­tled. In Flori­da v. J.L., the Supreme Court sug­gest­ed that an anony­mous tip may allege dan­ger so great—such as an immi­nent bomb—as to jus­ti­fy a Ter­ry frisk with a dimin­ished show­ing of reli­a­bil­i­ty.15 The Court fur­ther not­ed in City of Indi­anapo­lis v. Edmond that, although vehi­cle check­points for nar­cot­ic search­es are uncon­sti­tu­tion­al, check­points may be per­mis­si­ble in the con­text of thwart­ing an immi­nent ter­ror­ist attack or spe­cif­ic dan­ger­ous sus­pect.16 The Court cau­tioned, how­ev­er, that “[t]he grav­i­ty of the threat alone can­not be dis­pos­i­tive of ques­tions con­cern­ing what means law enforce­ment offi­cers may employ to pur­sue a giv­en pur­pose.”17 These cas­es sug­gest the nature of ter­ror­ism alle­ga­tions may be rel­e­vant to, but not inde­pen­dent­ly estab­lish, prob­a­ble cause.

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Gen­er­al­ized alle­ga­tions of terrorism—such as stock­pil­ing weapons in con­nec­tion with ter­ror­ist propaganda—made by an accused’s for­mer spouse and only cor­rob­o­rat­ed by a records check of the accused should fail to sup­port a find­ing of prob­a­ble cause.

First, uncor­rob­o­rat­ed and gen­er­al­ized alle­ga­tions of ter­ror­ism lodged by the accused’s for­mer spouse sup­port at most a min­i­mal show­ing of verac­i­ty. This is espe­cial­ly true where the alle­ga­tions refer to pro­pa­gan­da post­ed on social media and law enforce­ment fails to sub­stan­ti­ate the exis­tence of those posts. Law enforce­ment rou­tine­ly access­es social media posts direct­ly or through the assis­tance of infor­mants, and the fail­ure of law enforce­ment to attempt these inves­tiga­tive mea­sures or obtain cor­rob­o­rat­ing evi­dence through social media search­es should be con­sid­ered as part of the “total­i­ty of the cir­cum­stances.”18

Sec­ond, a strong basis of knowl­edge can­not be inferred from even a tipster’s for­mer mar­i­tal rela­tion­ship to the accused.19 Indeed, this type of rela­tion­ship expos­es a risk that the alle­ga­tions are “shad­ed or inac­cu­rate” and pro­voked by per­son­al rea­sons.20 This risk is par­tic­u­lar­ly strong where the infor­mant and accused may have chil­dren togeth­er or share finan­cial oblig­a­tions.21 As the Sev­enth Cir­cuit has found, an informant’s per­son­al or “finan­cial motive” in the case may weigh heav­i­ly in deter­min­ing even a known informant’s reli­a­bil­i­ty.22

Third, the Supreme Court has stat­ed that a defi­cien­cy in verac­i­ty or basis of knowl­edge can only be over­come by a “strong show­ing as to anoth­er” indi­cia of reli­a­bil­i­ty.23 A record check of the accused, how­ev­er, should be found insuf­fi­cient to estab­lish such strong alter­na­tive indi­cia of reli­a­bil­i­ty or to inde­pen­dent­ly estab­lish prob­a­ble cause. Unre­lat­ed pri­or con­vic­tions or out­stand­ing war­rants have nev­er before been found suf­fi­cient to estab­lish prob­a­ble cause to search; to do so would evis­cer­ate Fourth Amend­ment pro­tec­tions by mak­ing mil­lions of Amer­i­cans’ homes sub­ject to intru­sive search­es. As Jus­tices Sotomay­or and Gins­burg have rec­og­nized, the states and fed­er­al gov­ern­ment have expan­sive and out­dat­ed records of out­stand­ing war­rants that, if used to sup­port future arrests and con­vic­tions, could be called upon selec­tive­ly and pose the risk of wrong­ful depri­va­tion of indi­vid­u­als’ lib­er­ties.24 At most, the exis­tence or absence of an accused’s crim­i­nal records should be con­sid­ered one fac­tor among many in deter­min­ing prob­a­ble cause.25

Fourth, the nature of ter­ror­ism alle­ga­tions should not be dis­pos­i­tive to the prob­a­ble cause cal­cu­lus. To hold oth­er­wise would encour­age harass­ment by false reports of terrorism—that would require less cor­rob­o­ra­tion or knowl­edge of the informant—without enhanc­ing the reli­a­bil­i­ty of infor­ma­tion in the war­rant appli­ca­tion. While acknowl­edg­ing the pos­si­bil­i­ty of an exi­gency excep­tion to Ter­ry based on ter­ror­ism, the Court in J.L. ulti­mate­ly rea­soned that requir­ing a low­er stan­dard of reli­a­bil­i­ty for alle­ga­tions of more dan­ger­ous crimes would invite harass­ment through false report­ing of those offens­es to law enforce­ment.26 Jus­tice Gins­burg, in an unan­i­mous opin­ion for the Court, explained that it “would enable any per­son seek­ing to harass anoth­er to set in motion an intru­sive, embar­rass­ing police search of the tar­get­ed per­son . . . sim­ply by plac­ing an anony­mous call . . . ” In rea­son­ing equal­ly applic­a­ble to spe­cial needs search­es and prob­a­ble cause war­rants, the Edmond Court fur­ther cau­tioned that “the grav­i­ty of the threat alone can­not be dis­pos­i­tive.”27 Ulti­mate­ly, war­rants “should not be autho­rized unless there is some assur­ance that the infor­ma­tion on which they are based has been obtained in a reli­able way by an hon­est or cred­i­ble per­son.”28

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The Supreme Court in Gates moved away from a rigid for­mu­la of prob­a­ble cause and toward a fact-inten­sive inquiry under “the total­i­ty of the cir­cum­stances.” Although no longer required in every case, strong verac­i­ty and basis of knowl­edge remain impor­tant fac­tors in a prob­a­ble cause analy­sis that can only be dis­placed by equal­ly strong alter­na­tive indi­cia of reli­a­bil­i­ty. Where there is an alle­ga­tion of ter­ror­ism with weak verac­i­ty and the basis of knowl­edge must be inferred from the informant’s pri­or mar­riage to the accused, the accused’s crim­i­nal record and the nature of the threat alleged should not con­sti­tute strong indi­cia of reli­a­bil­i­ty suf­fi­cient to estab­lish prob­a­ble cause.


1. Daniel Kugler is a 3L at New York Uni­ver­si­ty School of Law. This piece is a com­men­tary on a prob­lem writ­ten for the 2018 Her­bert Wech­sler Nation­al Crim­i­nal Moot Court Com­pe­ti­tion at the Uni­ver­si­ty of Buf­fa­lo School of Law. The issue pre­sent­ed in the prob­lem focused on whether a search warrant—consisting of ter­ror­ism alle­ga­tions made by the defendant’s for­mer wife and the defendant’s crim­i­nal records—contained prob­a­ble cause under Illi­nois v. Gates, 462 U.S. 213 (1983) and suf­fi­cient verac­i­ty under Franks v. Delaware, 438 U.S. 154 (1978), despite the affiant’s inclu­sion of false infor­ma­tion and omis­sion of mate­r­i­al facts.

2. U.S. Con­st. amend. IV.

3. Illi­nois v. Gates, 462 U.S. 213, 238 (1983).

4. Gates, 462 U.S. at 230.

5. Id.

6. Id. at 216, 230, 238; see gen­er­al­ly Aguilar v. Texas, 378 U.S. 108 (1964); Spinel­li v. Unit­ed States, 393 U.S. 410 (1969).

7. Gates, 462 U.S. at 244–45 (“cor­rob­o­ra­tion through oth­er sources of infor­ma­tion [can] reduce[] the  chances of a reck­less or pre­var­i­cat­ing tale” (quot­ing Jones v. Unit­ed States, 362 U.S. 257, 271 (1960))).

8. See About Pub­lic and Pro­tect­ed Tweets, Twit­ter, (last vis­it­ed Feb­ru­ary 18, 2018).

9. See, e.g., Unit­ed States v. Meregildo, 883 F. Supp. 2d 523, 526 (S.D.N.Y. 2012) (uphold­ing prob­a­ble cause of search war­rant based on gov­ern­ment access to defendant’s Face­book pro­file); Per­ry v. Mont­gomery, No. CV-16–03730-FMO (KES), 2017 U.S. Dist. LEXIS 95077, at *35 (C.D. Cal. June 5, 2017) (find­ing no Fourth Amend­ment vio­la­tion by con­fi­den­tial informant’s war­rant­less seizure of suspect’s Insta­gram photo).

10. See Unit­ed States v. Fly­nn, 664 F.2d 1296, 1302-03 (5th Cir.), cert. denied, 456 U.S. 930 (1982).

11. Id.

12. Unit­ed States v. Hicks, No. 5:12-CR-00006-TBR, 2012 U.S. Dist. LEXIS 137189, at *12 (W.D. Ky. Sep. 24, 2012) (revers­ing prob­a­ble cause find­ing and giv­ing no weight to uncor­rob­o­rat­ed tip by defendant’s ex-wife that made gen­er­al alle­ga­tions that defendant’s com­put­er had viewed child pornog­ra­phy); see, e.g., Unit­ed States v. Peck, 317 F.3d 754, 757 (7th Cir. 2003) (find­ing no prob­a­ble cause where defendant’s girlfriend’s tip lacked “spe­cif­ic detail” about the drugs he pos­sessed, the loca­tion of drugs with­in his house, or his fre­quen­cy of drug deals, and police only cor­rob­o­rat­ed defendant’s crim­i­nal record).

13. Brine­gar v. Unit­ed States, 338 U.S. 160, 175–76 (1949).

14. Bur­rell v. McIl­roy, 464 F.3d 853, 858 n.3 (9th Cir. 2006) (find­ing that crim­i­nal his­to­ry “can­not alone estab­lish rea­son­able sus­pi­cion or prob­a­ble cause”) (cit­ing Brine­gar, 338 U.S. at 177 (1949)); see Peck, 317 F.3d at 757 (“[P]olice must do more than sim­ply run a record check of the accused, because this alone does not cor­rob­o­rate a CI’s state­ments alleg­ing that a search will uncov­er evi­dence of a crime.”).

15. Flori­da v. J.L., 529 U.S. 266, 273–74 (2000).

16. City of Indi­anapo­lis v. Edmond, 531 U.S. 32, 44 (2000).

17. Id. at 42.

18. See Meregildo, 883 F. Supp. 2d at 526; Per­ry, No. CV-16–03730-FMO (KES), at *35.

19. See Fly­nn, 664 F.2d at 1302-03.

20. See id.

21. See also Unit­ed States v. Grover, 755 F.3d 811, 817 (7th Cir. 2014) (find­ing informant’s “finan­cial motive” rel­e­vant to deter­min­ing prob­a­ble cause).

22. Id.

23. Gates, 462 U.S. at 230.

24. See Utah v. Stri­eff, 136 S. Ct. 2056, 2068 (2016) (Sotomay­or, J., dis­sent­ing) (“The States and Fed­er­al Gov­ern­ment main­tain data­bas­es with over 7.8 mil­lion out­stand­ing war­rants, the vast major­i­ty of which appear to be for minor offens­es.”); Her­ring v. Unit­ed States, 555 U.S. 135, 155 (2009) (Gins­burg, J., dis­sent­ing) (assert­ing that “[i]naccuracies in expan­sive, inter­con­nect­ed col­lec­tions of elec­tron­ic infor­ma­tion,” includ­ing out­stand­ing war­rants, “raise grave con­cerns for indi­vid­ual liberty”).

25. See Brine­gar, 338 U.S. at 175–76 (find­ing the arrest­ing officer’s arrest of the defen­dant for the same crime months ear­li­er rel­e­vant to deter­min­ing prob­a­ble cause); Bur­rell, 464 F.3d at 858 n. 3 (find­ing crim­i­nal records alone insuf­fi­cient for prob­a­ble cause); Peck, 317 F.3d at 757 (find­ing a check of the accused’s crim­i­nal record insuf­fi­cient cor­rob­o­ra­tion to estab­lish prob­a­ble cause).

26. J.L., 529 U.S. at 272–73 (“Such an [auto­mat­ic firearm] excep­tion [to Ter­ry reli­a­bil­i­ty analy­sis] would enable any per­son seek­ing to harass anoth­er to set in motion an intru­sive, embar­rass­ing police search of the tar­get­ed per­son sim­ply by plac­ing an anony­mous call false­ly report­ing the tar­get’s unlaw­ful car­riage of a gun.”).

27. Edmond, 531 U.S. at 42.

28. Gates, 462 U.S. at 283.