The seventh-circuit affirmed the defendant’s conviction for conspiracy and distribution of cocaine, holding that while the district court committed reversible error by admitting evidence of a prior heroin sale under Federal Rule of Evidence 404(b), the error was harmless given the overwhelming evidence of guilt. The court applied the standard that Rule 404(b) prohibits using other-act evidence to prove a defendant’s propensity to commit crimes, requiring instead a propensity-free chain of reasoning for non-propensity purposes such as knowledge or intent. The court reasoned that because cocaine and heroin are distinct substances and the defendant did not contest his knowledge or intent at trial—focusing solely on drug quantity—the admission of the heroin evidence relied on a forbidden propensity inference and its probative value was substantially outweighed by unfair prejudice under Rule 403. However, applying the harmless error test, the court found that the government’s case included compelling direct evidence such as recorded conversations, physical seizure of over five kilograms of cocaine, and the defendant’s post-arrest admissions, rendering the exclusion of the heroin evidence unlikely to have changed the jury’s verdict. Additionally, the court rejected the defendant’s claim that the prosecutor’s rebuttal argument violated his Fifth Amendment right against self-incrimination by commenting on his failure to testify, determining that the statement was a proper response to the defense’s closing argument and did not naturally remind the jury of the defendant’s silence, especially in light of curative jury instructions regarding the burden of proof. As a result, the judgment of the district court is affirmed and no new trial is ordered.