government experts's extensive prior teaching and/or consultancies, if they have been retained for a fee, sometimes can work to the detriment of the . example, experts who for a fee have done extensive training of investigtors and prosecutors of computer crime,and/or who have for a fee testified frequently for the prosecution in such, but not for the defense, could be impeached for bias and/or financial interest if the government calls then as expert witnesses. especially when a substantial part of an expert's income derives from such services to law enforcement, his comparative usefulness as an expert witness may be compromised.