In Preparing and Presenting Expert Testimony, traffic engineer and accident reconstruction expert witness Lawrence Levine writes:
Enough cannot be said about this conflict between expert engineer and his employer (in the case of an agency) or the party to which he consults. The most valuable information an expert can give an attorney is first, to be absolutely and completely honest about all aspects of a case. It is very rare that there are not two sides to an issue. This is where the judge and jury come into play; they are the final arbiters. Their task is to determine which facts are to be accepted and which information is to be ignored, and the amount weight to be given to each expert’s opinion.
However, it is essential that the lawyer know and trust in his expert’s “unbiased” and “unlimited” view of the case. Agencies may try to save money by using in-house personnel as expert witnesses on cases, but this should be approached with great caution. After all, this same expert could have some involvement in the creation of the situation, and certainly has a stake in the outcome. This bias hurts the agency’s reputation or costs them funding resources. Also the expert employee who wishes to protect their employer may approach a case with tunnel vision and thereby limit the agency attorney’s view of the case, both good and bad. The reason why most agencies seek outside consultants is to ensure an unbiased view of the case.