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1. Cross-Examination of Expert
Witnesses
Michael DeBlis III, Esq.

2. Rule 702. Testimony by Experts
• If scientific, technical, or other specialized
knowledge will assist the trier of fact to
understand the evidence or to determine a fact in
issue, a witness qualified as an expert by
knowledge, skill, experience, training, or
education, may testify thereto in the form of an
opinion or otherwise, if (1) the testimony is based
upon sufficient facts or data, (2) the testimony is
the product of reliable principles and methods,
and (3) the witness has applied the principles and
methods reliably to the facts of the case

3. FRYE and DAUBERT tests

4. The “Sniffer” Machine
• Dr. Vass and his laboratory stand to make a fortune
selling their contraption of a smell machine to law
enforcement across the country. If this judge allows it
in the case, many people including Dr. Vass stand to
make a lot of money. Never before has a judge allowed
it, but these people know that they have a damn good
chance with this particular judge allowing this machine
to be used in trial. Once Vass’s machine is used in trial,
it validates and elevates the value of Vass’s invention.
He and the lab can then sell it to every police
department in the nation. When that happens, they
are off to the races with the U.S. Patent Office with Dr.
Vass’s machine.

5. What does all this mean to us in a
courtroom?
• Expansion of pre-trial motions
• Expansion of voir dire of experts
• Real investigation of the science and the
scientist

6. Challenging the expert
• Either as to his or her credentials
• The "expertise" itself
• Use MOTIONS
– You might not be able to keep out the testimony,
but you may be able to limit it

7. Don’t ignore investigating and
challenging the expert
• Challenging the credentials
• Three types of experts
– Highly trained
– On-the-job
– Dubious training/dubious area

8. Strategy Considerations

9. Preparation of expert cross
• Learn something about the area
– Inbau & Moensens, Scientific Evidence in Criminal
Cases
• Use the phone
• Get TRANSCRIPTS
• Research
– College texts
– Read everything their expert has written

10. Interview the Expert Yourself

11. Experts and Language
• Learn theirs
• Learn to translate for jury
• Don't patronize

12. Basic Principles
• Normal principles of cross apply
• Extensive preparation essential
• Only ask leading questions
• One fact per question
• Never ask a question to which you do not
know the answer
• Develop a system with that you are
comfortable with

13. Special Problems When Witness Is an
Expert
• Witness is an expert in the field – you are not
• Witness is more difficult to control than a lay
witness
• Witness is likely well-educated and articulate
• Witness is experienced at courtroom
testimony

14. Examples of Cross-Examination of
Experts
• Forensic Pathologist in State v. Morehead
• Radiologist in State v. Carey
• Shaken baby syndrome experts in State v.
Carey

15. Forensic Pathologist
• State v. Morehead (client accused of strangling
grandmother)
– Defense was that grandmother died of heart
failure
– Cross-examination of medical examiner was
critical to outcome
– Examples of controlling the witness and learning
the terminology

16. Experts on the Shaken Baby Syndrome
• State v. Carey (client accused of shaking 5-
month old baby causing brain damage)
– Multiple expert witnesses for the state
– Cross of radiologist who reviewed CAT scan and
MRI
– Cross of non-treating outside expert on Shaken
Baby Syndrome

17. Cross-Examination
• What should jury feel about witness when you
are done?
– Is this good science?
– Can they trust the witness?
– Can they trust the evidence?
– Can they rely on the evidence?

18. Examine Bias
• Who do they testify for?
• Follow the money
• Membership in groups
• Built-in personal bias

19. Challenging the result
• Things not done cross
• Result is not OBJECTIVE
• Levels of certainty

20. Use demonstrative aids

21. Cross by learned treatise

22. The Ten Principles of Preparation for
Cross of an Expert
• (1) Identify opinions that have to be
challenged
• (2) Assemble all materials needed for cross-
examination
• (3) Obtain complete CV of opposing expert
• (4) Research expert’s prior testimony
• (5) Investigate allegations of mistake or
misconduct

23. The Ten Principles of Preparation for
Cross of an Expert
• (6) Research treatises and articles pertinent to
the subject matter
• (7) Retain an expert
• (8) Meet with opposing expert before trial
• (9) Learn the pertinent terminology in the
subject matter
• (10) Develop a system to organize your cross-
examination