What is the test for establishing that a single defendant has a "slight" connection to a conspiracy?

"Once existence of a conspiracy has been established, evidence of only a slight connection to the conspiracy is necessary in order to convict any one defendant of knowing participation in it." United States v. Berberian, 851 F.2d 236, 238 (9th Cir.1988) (citations omitted), cert. denied, 489 U.S. 1096 (1989). "Proof of a particular defendant's connection to the conspiracy can be established by circumstantial evidence." Id. "Of course, the 'slight' evidence must be of the quality which will reasonably support a conclusion that the particular defendant in question wilfully participated in the unlawful plan with the intent to further some object or purpose of the conspiracy. A common purpose and plan need not be proved by direct evidence but may be inferred from a 'development and collocation of circumstances.' " United States v. Freie, 545 F.2d 1217, 1222 (9th Cir.1976) (quoting Glasser v. United States, 315 U.S. 60, 80 (1942)), cert. denied, 430 U.S. 966 (1977).