both relevant and essential to the presentation of his case on the merits, see United States v. Russotti, 746 F.2d 945, 949-50 (2d Cir.1984), and that the need for disclosure outweighs the need for secrecy, United States v. Lilla, 699 F.2d 99, 105 (2d Cir. 1983); United States v. Manley, 632 F.2d 978, 985 (2d Cir.1980), cert.0 denied, 449 U.S. 1112, 101 S.Ct. 922, 66 L.Ed.2d 841 (1981); In re United States, 565 F.2d 19, 22-23 (2d Cir.1977), cert. denied, 436 U.S. 962, 98 S.Ct. 3082, 57 L.Ed.2d 1129 (1978). “[Wholesale disclosure” and “fishing expedition[s]” will normally be inappropriate. Id. at 23-24. As is true with respect to requests for disclosure of grand jury materials, the availability of other means for discovery or investigation, such as depositions or interviews, even if more expensive, weighs against disclosure, see Black v. Sheraton Corp. of America, 564 F.2d 550, 555 (D.C.Cir.1977); Hodgson v. Charles Martin Inspectors of Petroleum, Inc., 459 F.2d 303, 307 (5th Cir.1972), as does the possibility of economic retaliation against the informant, particularly where he is an employee of the target of the investigation, see In re United States, 565 F.2d at 22; Hodgson v. Charles Martin Inspectors of Petroleum, Inc., 459 F.2d at 307; Secretary of Labor v. Superior Care, Inc., 107 F.R.D. 395, 397 (E.D.N.Y.1985), or has been assured by a law enforcement official that his identity will not be disclosed, see Michelson v. Daly, 590 F.Supp. 261, 265 (N.D.N.Y.1984), appeal dismissed on procedural grounds sub nom. Estis v. Daly, 755 F.2d 913 (2d Cir.1985).
Here too, the district court has considerable discretion in determining whether disclosure is appropriate, United States v. Lilla, 699 F.2d at 105; United States v. Manley, 632 F.2d at 985; United States v. Hyatt, 565 F.2d 229, 231 (2d Cir. 1977), and in a civil case, the court’s denial of discovery based on the informer’s privilege will be overturned only if it is an abuse of discretion and has resulted in substantial prejudice, see Ghandi v. Police Dept. of City of Detroit, 747 F.2d 338, 354 (6th Cir.1984); cf. In re United States, 565 F.2d at 22 (“strength of the privilege is greater in civil litigation than in criminal”).
In the present case, in light of the extreme breadth of plaintiffs’ request, the availability of alternative means of obtaining the information, the potential for retaliation against the interviewees, and the assurances of confidentiality given by the FBI to obtain the interviews, we find no abuse of discretion in the court’s denial of plaintiffs’ request.
B. Exclusion from Evidence of the Margiotta Conviction
Prior to trial, plaintiffs sought a ruling that they would be allowed to introduce into evidence at trial the fact that Joseph M. Margiotta, Jr., Chairman of the County Committee and then a defendant in the case, had been convicted of a felony by reason of his requiring insurance agents doing business with the County to pay a portion of their commissions to the Republican Party in order to be allowed to continue doing such business. See United States v. Margiotta, 688 F.2d 108 (2d Cir.1982), cert. denied, 461 U.S. 913, 103 S.Ct. 1891, 77 L.Ed.2d 282 (1983). The court excluded the evidence on the ground that it might be used by the jury against defendants other than the County without a showing of connection to them and because the jury might confuse the fear of the insurance brokers in Margiotta with the alleged fear of the employees in the present action. Plaintiffs challenge this ruling, arguing that the Margiotta conviction was evidence of prior acts tending to establish that it was a custom or policy of the County to condition employment benefits on payments to the Republican Party. We find no basis for reversal.
Even where evidence of similar acts is relevant under Fed.R.Evid. 404(b), the trial court is required by Fed.R.Evid. 403 to weigh the probative value of the evidence against the potential for, inter alia, undue prejudice and jury confusion. The court is accorded broad discretion to exclude relevant evidence if the probative value is substantially outweighed by the