Sense-making software for crime investigation: how to combine stories and arguments? Henry Prakken (& Floris Bex, Susan van den Braak, Herre van Oostendorp, Bart Verheij, Gerard Vreeswijk) New York, January 29th, 2007

Contents A research project: Building software that supports crime investigators Investigate theoretical basis Stories and causality in evidential reasoning Abduction Reasoning with testimonies: Argumentation Combining stories and testimonies: abduction + argumentation

Practical motivation Crime investigation often one-sided, aiming to confirm a certain hypothesis Dutch criminal procedure is inquisitory: Judges rely on police case files Very little investigation in court... So a lot can go wrong

The intended software: a sense-making system No knowledge inside, but Supports human users in structuring and visualising their thinking Can calculate with these structures Can link them with case files Should be based on an account of evidentiary reasoning that is: Prescriptive (supporting rational thinking) Natural (close to the way crime investigators think)

Anchored Narratives Theory (Crombag, van Koppen & Wagenaar) A rational and natural theory of evidentiary reasoning? Recognises importance of stories (timelines!) Generalisations Find plausible causal links within story Anchor stories in evidence But theoretically underdeveloped Our aim: investigate theoretical foundations of ANT Causation Testimonies

Stories involve causation Stories are (at least) a sequence of events on a timeline Events are supposedly caused by earlier events Physical causation Mental causation Reasoning with causal information: Prediction: assume or observe event, predict what will happen next Explanation: observe event, explain what could have caused it

Example: the King case (1) Fact: King was beaten up by mr. Zomerdijk in backyard of Zomerdijks house Prosecutions story King (a convicted thief) was up to no good King climbs into backyard of Zomerdijk family King enters bedroom King steps on toy Mr. Zomerdijk hears sound Mr. Zomerdijk goes to bedroom King closes door and runs away

Example: the King case (2) Fact: King was beaten up by mr. Zomerdijk in backyard of Zomerdijks house Defences story King climbs into backyard of Zomerdijk family Wind opens bedroom door Wind hits toy Mr. Zomerdijk hears sound Mr. Zomerdijk goes to bedroom Mr. Zomerdijk sees King in backyard

Representing causal knowledge Explanation with evidential rules: Deduction: Explanation with causal rules: Abduction: Effect Cause Effect Cause Cause Effect Effect Cause Fire causes Smoke Smoke Fire Smoke means Fire Smoke Fire

Abductive-logical models Simulate abduction with deduction: Given: causal rules T explanandum F Hypothesise a cause C such that T with C logically implies F (C explains F) Compare all alternative explanations How much additional evidence is explained? How much additional evidence is contradicted? …

Explanations as causal networks of events Toy makes a sound Observations The door is closed

Explanations as causal networks of events Toy makes a sound Observations The door is closed King enters house King steps on toy King closes door

Explanations as causal networks of events Toy makes a sound Observations The door is closed King enters house King steps on toy King closes door The wind hits the toy The wind closes the door The wind opens the door Loud bang

Explanations as causal networks of events Toy makes a sound Observations The door is closed King enters house King steps on toy King closes door No loud bang was heard The wind hits the toy The wind closes the door The wind opens the door Loud bang

A problem(?): testimonies must also be explained King enters house King steps on toy Toy makes a sound Observations The door is closed King closes door Witness wants to protect himself Witness Z often imagines sounds Witness Z says I heard a sound Witness Z says the door was closed

Testimony principle is not a causal but an evidential rule Testimony principle not represented from-cause-to- effect: but from-cause-to-effect: Truth of P is the usual cause of P. Other causes of are exceptions. Reasoning is then modelled as constructing and comparing (defeasible) arguments Witness says P => P P => Witness says P

Combining abduction and argumentation Toy makes a sound Observations The door is closed King enters house King steps on toy King closes door Witness Z says I heard a sound Witness Z is not sincere Witness wants to protect himself Further evidence needed!

The full picture Toy makes a sound Observations The door is closed King enters house King steps on toy King closes door No loud bang was heard The wind hits the toy The wind closes the door The wind opens the door Loud bang

Conclusion Combining abduction for representing stories and argumentation for reasoning about sources of evidence arguably is natural can arguably be given a sound rational basis But all this should be further investigated

Arguments Assault e1e1 e3e3 e2e2 hitting p intent

Counterarguments Assault e1e1 e3e3 e2e2 hitting p intent Selfdefence attacked e4e4 e5e5 q

Reinstatement Assault e1e1 e3e3 e2e2 hitting p intent Selfdefence attacked e4e4 e5e5 q Not attacked e6e6 e7e7