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Page Number: 289.0

128 

McDANIEL  v.  BROWN 

Per Curiam 

The prosecutor’s fallacy is the assumption that the random 
match probability is the same as the probability that the de­
fendant  was  not  the  source  of  the  DNA  sample.  See  Nat. 
Research  Council,  Comm.  on  DNA  Forensic  Science,  The 
Evaluation  of  Forensic  DNA  Evidence  133  (1996)  (“Let  P 
equal  the  probability  of  a  match,  given  the  evidence  geno­
type.  The fallacy is to say that P is also the probability that 
the  DNA  at the  crime  scene  came  from someone  other  than 
the defendant”).  In other words, if a juror is told the proba­
bility  a  member  of  the  general  population  would  share  the 
same DNA is 1 in 10,000 (random match probability), and he 
takes  that  to  mean  there  is  only a 1 in  10,000  chance  that 
someone other than the defendant is the source of the DNA 
found  at  the  crime  scene  (source  probability),  then  he  has 
succumbed to the prosecutor’s fallacy.  It is further error to 
equate  source  probability  with  probability  of  guilt,  unless 
there  is  no  explanation  other  than  guilt  for  a  person  to  be 
the source of crime-scene DNA.  This faulty reasoning may 
result  in  an  erroneous  statement  that,  based  on  a  random 
match probability of 1 in 10,000, there is a 0.01% chance the 
defendant  is  innocent  or  a  99.99%  chance  the  defendant  is 
guilty. 

The  Mueller  Report  does  not  dispute  Romero’s  opinion 
that  only  1  in  3  million  people  would  have  the  same  DNA 
proﬁle as the rapist.  Mueller correctly points out, however, 
that some of Romero’s testimony—as well as the prosecutor’s 
argument—suggested that the evidence also established that 
there was only a 0.000033% chance that respondent was inno­
cent.  The  State  concedes  as  much.  Brief  for  Petitioners 
54.  For  example, the  prosecutor  argued at  closing the  jury 
could  be  “99.999967  percent  sure”  in  this  case.  App.  730. 
And when the prosecutor asked Romero, in a classic example 
of  erroneously  equating  source  probability  with  random 
match probability, whether “it [would] be fair to say . . .  that 
the  chances  that  the  DNA  found  in  the  panties—the  semen