Cite as: 555 U. S. ____ (2008) 1 

ROBERTS, C. J., dissenting 

SUPREME COURT OF THE UNITED STATES 

PENNSYLVANIA v. NATHAN DUNLAP 

ON PETITION FOR WRIT OF CERTIORARI TO THE SUPREME 

COURT OF PENNSYLVANIA, EASTERN DISTRICT

No. 07–1486. Decided October 14, 2008 

The petition for a writ of certiorari is denied. 

CHIEF JUSTICE ROBERTS, with whom JUSTICE KENNEDY 

joins, dissenting from denial of certiorari. 

North Philly, May 4, 2001. Officer Sean Devlin, Narcotics Strike Force, was working the morning shift. Undercover surveillance. The neighborhood? Tough as a threedollar steak. Devlin knew. Five years on the beat, nine 

months with the Strike Force. He’d made fifteen, twenty 

drug busts in the neighborhood. 

Devlin spotted him: a lone man on the corner. Another 

approached. Quick exchange of words. Cash handed over; 

small objects handed back. Each man then quickly on his 

own way. Devlin knew the guy wasn’t buying bus tokens. 

He radioed a description and Officer Stein picked up the

buyer. Sure enough: three bags of crack in the guy’s 

pocket. Head downtown and book him. Just another day 

at the office. 

* * * 

That was not good enough for the Pennsylvania Supreme Court, which held in a divided decision that the 

police lacked probable cause to arrest the defendant. The 

Court concluded that a “single, isolated transaction” in a

high-crime area was insufficient to justify the arrest, given

that the officer did not actually see the drugs, there was

no tip from an informant, and the defendant did not attempt to flee. 941 A. 2d 671, 679 (2007). I disagree with

that conclusion, and dissent from the denial of certiorari. 

A drug purchase was not the only possible explanation for 

the defendant’s conduct, but it was certainly likely enough 
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ROBERTS, C. J., dissenting 

to give rise to probable cause. 

The probable-cause standard is a “nontechnical conception that deals with the factual and practical considerations of everyday life on which reasonable and prudent 

men, not legal technicians, act.” Maryland v. Pringle, 540 

U. S. 366, 370 (2003) (internal quotation marks omitted). 

What is required is simply “a reasonable ground for belief

of guilt,” id., at 371 (same)—a “probability, and not a

prima facie showing, of criminal activity,” Illinois v. Gates, 

462 U. S. 213, 235 (1983) (same). “[A] police officer may

draw inferences based on his own experience in deciding 

whether probable cause exists,” Ornelas v. United States, 

517 U. S. 690, 700 (1996), including inferences “that might 

well elude an untrained person,” United States v. Cortez, 

449 U. S. 411, 418 (1981).

On the facts of this case, I think the police clearly had 

probable cause to arrest the defendant. An officer with 

drug interdiction experience in the neighborhood saw two

men on a street corner—with no apparent familiarity or 

prior interaction—make a quick hand-to-hand exchange of 

cash for “‘small objects.’” 941 A. 2d, at 673. This exchange took place in a high-crime neighborhood known for

drug activity, far from any legitimate businesses. Perhaps

it is possible to imagine innocent explanations for this 

conduct, but I cannot come up with any remotely as likely 

as the drug transaction Devlin believed he had witnessed.

In any event, an officer is not required to eliminate all

innocent explanations for a suspicious set of facts to have

probable cause to make an arrest. As we explained in 

Gates, “[i]n making a determination of probable cause the

relevant inquiry is not whether particular conduct is

‘innocent’ or ‘guilty,’ but the degree of suspicion that attaches to particular types of noncriminal acts.” 462 U. S., 

at 244, n. 13. 

The Pennsylvania Supreme Court emphasized that the

police did not actually see any drugs. 941 A. 2d, at 679. 
Cite as: 555 U. S. ____ (2008) 3 

ROBERTS, C. J., dissenting 

But Officer Devlin and his partner were conducting undercover surveillance. From a distance, it would be difficult to have a clear view of the small objects that changed 

hands. As the Commonwealth explains in its petition for 

certiorari, the “classic” drug transaction is a hand-to-hand 

exchange, on the street, of cash for small objects. Pet. for 

Cert. 5–8. The Pennsylvania Supreme Court’s decision 

will make it more difficult for the police to conduct drug 

interdiction in high-crime areas, unless they employ the

riskier practice of having undercover officers actually

make a purchase or sale of drugs.

The Pennsylvania Court also noted that the defendant 

did not flee. 941 A. 2d, at 671. Flight is hardly a prerequisite to a finding of probable cause. A defendant may

well decide that the odds of escape do not justify adding

another charge to that of drug possession. And of course 

there is no suggestion in the record that the defendant had 

any chance to flee—he was caught redhanded. 

Aside from its importance for law enforcement, this

question has divided state courts, a traditional ground 

warranting review on certiorari. S. Ct. Rule 10(b). The 

New Jersey Supreme Court has held that an “experienced

narcotics officer” had probable cause to make an arrest 

when—in a vacant lot in a high-drug neighborhood—he 

“saw defendant and his companion give money to [a] third

person in exchange for small unknown objects.” State v. 

Moore, 181 N. J. 40, 46–47, 853 A. 2d 903, 907 (2004). The 

Rhode Island Supreme Court reached the same conclusion

in a case where the defendants—through their car windows—exchanged cash for a small “bag of suspected narcotics.” State v. Castro, 891 A. 2d 848, 851–854 (2006). In 

contrast, the Colorado Supreme Court held that a hand-tohand exchange of unknown objects did not give the police 

probable cause to make an arrest, even where one of the

men was a known drug dealer. People v. Ratcliff, 778 

P. 2d 1371, 1377–1378 (1989). All these cases have unique 
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ROBERTS, C. J., dissenting 

factual wrinkles, as any probable-cause case would, but 

the core fact pattern is the same: experienced police officers observing hand-to-hand exchanges of cash for small,

unknown objects in high-crime neighborhoods.

The Pennsylvania Supreme Court speculated that such

an exchange could have been perfectly innocent. But as 

Judge Friendly has pointed out, “[j]udges are not required to 

exhibit a naiveté from which ordinary citizens are free.” 

United States v. Stanchich, 550 F. 2d 1294, 1300 (CA2 

1977). Based not only on common sense but also his experience as a narcotics officer and his previous work in the

neighborhood, Officer Devlin concluded that what happened

on that street corner was probably a drug transaction. That 

is by far the most reasonable conclusion, even though our

cases only require it to be a reasonable conclusion. 

I would grant certiorari and reverse the judgment of the 

Pennsylvania Supreme Court.