HERRMANN, Chief Justice:

The defendant, Terry Wheatley, appeals his conviction of two counts of delivering cocaine. 16 Del. C. § 4716, 4751(b). He contends that the Trial Court committed reversible error (1) in refusing his request for a missing-witness instruction; and (2) in denying his motion for a mistrial based upon alleged prosecutorial misconduct.

I.

At trial, during his opening statement, the prosecutor informed the jury that cocaine was sold by the defendant on three occasions, to a "reliable, confidential, informer." The informer was not called as a witness by the State, nor subpoenaed by the defendant. Upon the contention that the informer was known to the State but not to the defendant, the following jury instruction was requested by the defendant:

"If there is a witness that is only known to the State, that witness having material knowledge of the case, that witness if not called or subpoenaed by the State is said to be a missing witness. You are to presume that the testimony of any missing witness would be unfavorable to the side that did not call the missing witness; that is the State."

The Trial Court declined to give the instruction.

The defendant appeals on that ground, relying upon broad general rules on typical missing-witness instructions; e.g., 1 Wharton's Criminal Evidence, § 148, p. 249 (13th ed. 1972); 29 Am.Jur., 2d. Evidence, § 180, p. 224-5; 31A C.J.S., Evidence, § 156(1), p. 397.

The State contends that a missing-witness instruction, such as was sought here, violates Del. C.onst., Art. IV, § 19 because it amounts to an impermissible comment on the evidence, citing Boyer v. State, Del.Supr., 436 A.2d 1118, 1124 (1981). The defendant takes issue with that contention, seeking to distinguish Boyer on its facts; but, under the cardinal rule that constitutional questions will not be decided unless essential to the disposition of the case, we do not reach the constitutional question (including the applicability and viability of Boyer), since, as the State contends, the requested instruction was clearly impermissible under well-established non-constitutional concepts:

A missing-witness inference is permissible only where it would be "natural" for the party to produce the witness if his testimony would be favorable. The principle is stated in United States v. Tucker, (7 Cir.), 552 F.2d 202, 210 (1977), as follows:

". . . Like all sound inferences, the missing witness inference is rooted in notions of common sense, specifically that where a party fails to call an available witness with important and relevant knowledge, it may be that he has something to fear in the witness' testimony. The strength of the inference will, of course, vary with the facts of each case, depending on how natural it would be for the party to have called the witness but for some apprehension over his testimony. . . ."

The concept is stated in Wigmore Evidence on Trials at Common Law § 286 at p. 199 (Chadbourn rev. 1979), as follows:

"[i]t is plain that the inference is based, not on the bare fact that a particular person is not produced as a witness, but on his non-production when it would be natural for him to produce the witness if the facts known by him had been favorable."

In the instant case, the non-production of the informant by the State was a product not of the nature of his testimony but rather the status of his position. It would not be "natural" for the State to call the informant upon the facts and circumstances of this case. The identity of an informant is privileged under Delaware Uniform Rule of Evidence 509. The defendant made no effort to utilize the discovery provisions of D.R.E. 509 in order to learn the identity of the informant.

The basis of the privilege has been well stated as follows:

". . . Whether an informer is motivated by good citizenship, promise of leniency or prospect of pecuniary reward, he will usually condition his cooperation on an assurance of anonymity — to protect himself and his family from harm, to preclude adverse social reactions and to avoid the risk of defamation or malicious prosecution actions against him. The government also has an interest in non-disclosure of the identity of its informers. Law enforcement officers often depend upon professional informers to furnish them with a flow of information about criminal activities. Revelation of the dual role played by such persons ends their usefulness to the government and discourages others from entering into a like relationship."

8 Wigmore (McNaughton rev. 1961) § 2374, at 761-762. See also State v. Flowers, Del.Super., 316 A.2d 564 (1973).

The policy considerations, implicit in the informant's privilege, justified the failure of the State to produce the informant as a witness in this case. The defendant, having failed to take advantage of the discovery process available under D.R.E. 509, has failed to show any reason sufficient to overcome the policy considerations here involved. Compare United States v. Busic, 3 Cir. 587 F.2d 577, 586-7 (1978). For that reason, the requested missing-witness instruction was inappropriate. It follows that there was no error in the Trial Court's denial of the requested instruction. "The important thing is the availability of discovery. If it is not employed, the party ought not be allowed to resort to the necessarily somewhat speculative inference when discovery would substitute certainty." McCormick's Handbook of the Law of Evidence, § 272, p. 675 (2nd ed., 1972); see also United States v. Kenny, (4 Cir.), 500 F.2d 39 (1974).

II.

The defendant also claims reversible error in the Trial Court's denial of his motion for mistrial, based upon the ground that the prosecutor made improper and prejudicial comments during his opening statement to the effect: (1) that there were three drug transactions during the evening in question, whereas the defendant was indicted for only two; and (2) that the defendant had an altercation with a co-defendant tried separately — hearsay at best. On the record before us, we find no abuse of discretion in the denial of the motion for mistrial. D.R.E. Rule 404(b).

* * *