# Banksy and the mathematicians

Assuming you’ve heard of Banksy (if not, he’s an internationally known graffiti artist), then you understand that no one knows his real name for certain although there are strong suspicions, as of 2008, that he is Robin Gunningham. It seems the puzzle has aroused scientific curiosity according to a March 4, 2016 article by Jill Lawless on CBC (Canadian Broadcasting Corporation) News online,

Elusive street artist Banksy may have been unmasked — by mathematics.

Scientists have applied a type of modelling used to track down criminals and map disease outbreaks to identify the graffiti artist, whose real name has never been confirmed.

The technique, known as geographic profiling, is used by police forces to narrow down lists of suspects by calculating from multiple crime sites where the offender most likely lives.

The March 3, 2016 article in The Economist about the Banksy project describes the model used to derive his identity in more detail,

Their system, Dirichlet process mixture modelling, is more sophisticated than the criminal geographic targeting (CGT) currently favoured by crime-fighters. CGT is based on a simple assumption: that crimes happen near to where those responsible reside. Plot out an incident map and the points should surround the criminal like a doughnut (malefactors tend not to offend on their own doorsteps, but nor do they stray too far). The Dirichlet model allows for more than one “source”—a place relevant to a suspect such as home, work or a frequent pit stop on a commute—but makes no assumptions about their number; it automatically parses the mess of crime sites into clusters of activity.

Then, for each site, it calculates the probability that the given array of activity, and the way it is clustered, would result from any given source. Through a monumental summing of probabilities across each and every possible combination of sources, the model spits out the most likely ones, with considerable precision—down to 50 metres or so in some cases.

While this seems like harmless mathematical modeling, Banksy lawyers were sufficiently concerned over how this work would be promoted that they contacted the publisher according to Jonathan Webb’s March 3, 2016 article for BBC (British Broadcasting Corporation) News online,

A study that tests the method of geographical profiling on Banksy has appeared, after a delay caused by an intervention from the artist’s lawyers.

Scientists at Queen Mary University of London found that the distribution of Banksy’s famous graffiti supported a previously suggested real identity.

The study was due to appear in the Journal of Spatial Science a week ago.

The BBC understands that Banksy’s legal team contacted QMUL staff with concerns about how the study was to be promoted.

Those concerns apparently centred on the wording of a press release, which has now been withdrawn.

Taylor and Francis, which publishes the journal, said that the research paper itself had not been questioned. It appeared online on Thursday [March 3, 2016] unchanged, after being placed “on hold” while conversations between lawyers took place.

The scientists conducted the study to demonstrate the wide applicability of geoprofiling – but also out of interest, said biologist Steve Le Comber, “to see whether it would work”.

The criminologist and former detective who pioneered geoprofiling, Canadian Dr Kim Rossmo [emphasis mine] – now at Texas State University in the US – is a co-author on the paper.

The researchers say their findings support the use of such profiling in counter-terrorism, based on the idea that minor “terrorism-related acts” – like graffiti – could help locate bases before more serious incidents unfold.

I believe the biologist Steve Le Comber is interested in applying the technique to epidemiology (study of patterns in health and disease in various populations). As for Dr. Rossmo, he featured in one of the more bizarre incidents in Vancouver Police Department (VPD) history as described in the Kim Rossmo entry on Wikipedia (Note: Links have been removed),

D. Kim Rossmo is a Canadian criminologist specializing in geographic profiling. He joined the Vancouver Police Department as a civilian employee in 1978 and became a sworn officer in 1980. In 1987 he received a master’s degree in criminology from Simon Fraser University and in 1995 became the first police officer in Canada to obtain a doctorate in criminology.[1] His dissertation research resulted in a new criminal investigative methodology called geographic profiling, based on Rossmo’s formula. This technology was integrated into a specialized crime analysis software product called Rigel. The Rigel product is developed by the software company Environmental Criminology Research Inc. (ECRI), which Rossmo co-founded.[2]

In 1995, he was promoted to detective inspector and founded a geographic profiling section within the Vancouver Police Department. In 1998, his analysis of cases of missing sex trade workers determined that a serial killer was at work, a conclusion ultimately vindicated by the arrest and conviction of Robert Pickton in 2002. A retired Vancouver police staff sergeant has claimed that animosity toward Rossmo delayed the arrest of Pickton, leaving him free to carry out additional murders.[3] His analytic results were not accepted at the time and after a dispute with senior members of the department he left in 2001. His unsuccessful lawsuit against the Vancouver Police Board for wrongful dismissal exposed considerable apparent dysfunction within that department.[1]

It’s still boggles my mind and the reporters covering story that the VPD would dismiss someone who was being lauded internationally for his work and had helped the department solve a very nasty case. In any event, Dr. Rossmo is now at Texas State University.

Getting back to Banksy and geographic profiling, here’s a link to and a citation for the paper,

Tagging Banksy: using geographic profiling to investigate a modern art mystery by Michelle V. Hauge, Mark D. Stevenson, D. Kim Rossmo & Steven C. Le Comber. Journal of Spatial Science DOI:  10.1080/14498596.2016.1138246 Published online: 03 Mar 2016

This paper is behind a paywall.

For anyone curious about Banksy’s work, here’s an image from this Wikipedia entry,

Stencil on the waterline of The Thekla, an entertainment boat in central Bristol – (wider view). The section of the hull with this picture has now been removed and is on display at the M Shed museum. The image of Death is based on a nineteenth-century etching illustrating the pestilence of The Great Stink.[19] Artist: Banksy – Photographed by Adrian Pingstone