•  Nardone v. United States (1937) has held that evidence obtained under an impermissible search is ‘fruit of the poisonous tree’ and is excluded from consideration.

• In 2016 Supreme Court decision, evidence seized through a search after an illegal stop conducted by law enforcement is now admissible upon discovery of a valid warrant after the fact

Utah v. Strieff

• “In practice encourages police officers to conduct illegal searches and seizures. To investigate a suspect, an officer needs only to stop a suspect, check their ID, and upon discovering a warrant are free to search him incident to arrest.” (Kerr and Howe 2016)

• The majority opinion reasoned that because the presence of an outstanding warrant is an “extraordinary intervening” circumstance, it severs the link between an illegal stop and a subsequent search.

Utah v. Strieff

Widespread municipal warrants and over-policing, especially in some neighborhoods,
mean Strieff-type stops are common,
not extraordinary

Hypothesis

• Detailed stop and warrant data is rare
• Different types of warrants
  • municipal warrant (majority of warrants in the United States)
    • running a red light. $300-800

Municipal Warrant

• Austin, Texas has a relative low ratio of warrants to population:
  7.7 / 100 residents.
• New York, NY:
  16 warrants / 100 residents
• St Louis, MO:
  99 warrants / 100 residents

 Warrant Prevalence In U.S. Cities Varies

Distribution of warrants per individual

If St. Louis has the same
distribution as Austin

If St. Louis has the same spatial distribution,
some neighborhoods have 100% prevalence

Title Text

Warrant prevalence ~ area income

Cruel nonsense

 Is A Strieff Police Stop an Extraordinary Circumstance?

Assume that the average number of Strieff stops is equal to

avg. number of police stops per zip code

ｘ

individuals with warrants / total population

 Strieff Hit Rate

• Specify λ - avg warrants per person *  stops
  • year
  • month
  • week
• chances that a draw from that Poisson distribution is greater than 0
• Then, calculate this probability of a Strieff stop in a given Austin neighborhood (zip code)

Simulate Likelihood of at Least One Strieff Stop

• Model individual level Strieff stop risk
• Conduct similar analysis in jurisdiction with higher warrant prevalence

Future Research

• Privacy concerns of open warrant data
• Targeted stops and citations for neighborhoods who cannot pay original fee
• Great Texas Roundup
• Debtors Prison

Ethical Implications

Spatial distribution