In a criminal case, is it possible that an expert in a field conducts cross-examination of a prosecution witness instead of the defence counsel?
Answer: Simple answer to your question is “No”. It is not permissible under law to allow an expert (other than an advocate) to conduct cross-examination of a witness or conduct the case in some other manner. Of course, if the accused himself wants to conduct his own case (including the cross-examination of prosecution witnesses) instead of engaging an advocate, he may do so. [In this regard, also see: (1) Do I have right to defend my own case in court without lawyer? (2) Can I argue or give clarification in a case when my lawyer is unable or confused to answer?]. However, the accused is not permitted to engage any other person, including an expert in a field, who is not an advocate, to conduct the case on his behalf such as cross-examination of a witness.
In this regard, reference may be made to Section 33 and Section 29 of the Advocates Act, 1961, which do not allow any person, other than an advocate, to practice law before any court or authority. These sections are reproduced below:
“33. Advocates alone entitled to practise.—Except as otherwise provided in this Act or in any other law for the time being in force, no person shall, on or after the appointed day, be entitled to practise in any court or before any authority or person unless he is enrolled as an advocate under this Act.
29. Advocates to be the only recognised class of persons entitled to practise law.—Subject to the provisions of this Act and any rules made thereunder, there shall, as from the appointed day, be only one class of persons entitled to practise the profession of law, namely, advocates.”
It may also be pertinent to point out that Section 303 of Cr.P.C. gives a right to the accused to be defended by a pleader (i.e., an advocate) of his choice, however, there is no provision giving him right to be defended by any other person who is not an advocate:
“303. Right of person against whom proceedings are instituted to be defended.— Any person accused of an offence before a Criminal Court, or against whom proceedings are instituted under this Code, may of right be defended by a pleader of his choice.”
Further, Section 304(1) of Cr.P.C. lays down that if the accused is not able to engage an advocate due to his financial difficulties, the Court is duty-bound to provide an advocate to him for his defence at the expense of the Government (legal aid):
“304. Legal aid to accused at State expense in certain cases.—(1) Where, in a trial before the Court of Session, the accused is not represented by a pleader, and where it appears to the Court that the accused has not sufficient means to engage a pleader, the Court shall assign a pleader for his defence at the expense of the State.”
Thus, as mentioned above, you can argue your case yourself instead of engaging an advocate. A party-in-person is allowed to present his case or argue his case himself, provided he has not engaged an advocate. But, it is not permissible to engage any person other than an advocate to conduct the case or argue the case in the court on behalf of some other person. This restriction applies also to an expert in a field. Of course, it may generally be permissible to keep an expert available in court, who may guide your advocate on certain aspects of the case, but the cross-examination will have to be conducted by the advocate and not by the expert.