From United States v. Abdallah, 2009 U.S. Dist. LEXIS 36172 (S.D. Tex. April 29, 2009):

[T]he Abdallahs argue that this court erred by failing to exclude Patterson from the courtroom, in violation of Rule 615 of the Federal Rules of Evidence. Rule 615 directs that upon a party's request or upon its own motion "the court shall order witnesses excluded so that they cannot hear the testimony of other witnesses" subject to certain exceptions. The exceptions include "(3) a person whose presence is shown by a party to be essential to the presentation of the party's cause." The Abdallahs contend that Patterson was not essential to the government's case because her testimony and opinion was redundant of Griffith's. Relying on Opus 3 Ltd. v. Heritage Park, Inc., 91 F.3d 625, 629 (4th Cir. 1996), the Abdallahs also contend that the exception does not apply to Patterson because she also served as a fact witness regarding disputed issues in the case.

The government responds that Patterson was appropriately allowed to listen to testimony because Federal Rule of Evidence 703 "provides that an expert may base his opinions on facts or data obtained 'at or before the hearing.'" Mayo v. Tri-Bell Industries, Inc., 787 F.2d 1007, 1013 (5th Cir. 1986). In Mayo, the court held that it was permissible for the defendant's expert witness to testify after having discussed the evidence with defense counsel during a break in trial. Citing Rule 703, the court concluded that expert witnesses "would be testifying solely as to their opinion based on the facts or data in the case, and, accordingly, were properly exempted from the order excluding witnesses. Because the experts were not witnesses whose recollections might have been colored by accounts of prior witnesses, there was no prejudice." ….

Some courts have rejected the government's argument that, consistent with Rule 703, Rule 615(3) does not cover expert witnesses who express opinions based on the facts of the case. See, e.g., Opus 3, 91 F.3d at 629; Woodson v. McGeorge Camping Ctr., Inc., 42 F.3d 1387, 1994 WL 667052, at *3 (4th Cir. 1994) (unpublished table decision); Miller v. Universal City Studios, Inc., 650 F.2d 1365, 1373-74 (5th Cir. 1981); Morvant v. Const. Aggregates Corp., 570 F.2d 626, 630 (6th Cir. 1978). In Miller, the Fifth Circuit agreed with the Morvant court that "Rule 703 does not furnish an automatic basis for exempting an expert from sequestration under rule 615 . . . . Whether or not it would be reasonable for a trial court to exempt an expert witness from a sequestration order, there is no required exemption implied under rule 615." 650 F.2d at 1374.

The Abdallahs' reliance on Opus 3 is misplaced. The district court excluded the witness in that case "not because he was an expert who would not benefit from testimony, but because he was a key fact witness." 91 F.3d at 629. Patterson was not a fact witness in this case, much less a key fact witness, but gave opinion testimony based on her review of the run sheets and medical records. Although Rule 703 does not provide a blanket exemption from Rule 615, Patterson was appropriately exempted from Rule 615 in this case, along with Dr. Evans, the Abdallahs' expert. Expert witnesses who either respond to the theories of an adversary's expert or base their opinions on facts adduced by witnesses at trial are infrequently excluded from the courtroom during trial. See Morvant, 570 F.2d at 629-30 ("Theoretically at least, the presence in the courtroom of an expert witness who does not testify to the facts of the case but rather gives his opinion based upon the testimony of others hardly seems suspect and will in most cases be beneficial, for he will be more likely to base his expert opinion on a more accurate understanding of the testimony as it evolves . . . ."). It is within the trial judge's discretion to except from the rule expert witnesses who may base their opinions in part on witness testimony. Id. at 630. Patterson was appropriately exempted from the Rule 615 order.