Normally, under Federal Rule of Evidence 404, evidence of other crimes, wrongs, or acts is not admissible to prove the character of a person in order to show action in conformity therewith.
Using the doctrine of chances allows a prosecutor to admit evidence of prior "accidents" that can persuade a jury that prior incidents are so similar that it is very improbable that the case at bar is actually accidental.
The doctrine of chances was first developed by English courts in the case Rex v. Smith, 11 Cr.
In this case the defendant was accused of murdering his wife by drowning her in a bath.
The prosecutor sought to include evidence in the trial that the defendant's two previous wives had both died in the same way.