Because inferences of guilt or innocence are drawn from the analysis of tangible things or circumstances, physical evidence is, by definition, circumstantial. For example, a suspect's latent fingerprint in safe insulation powder at the scene of a burglary is direct proof that the suspect was at the site after the safe had been broken into. That the suspect is the safe burglar requires an inference; this requirement makes the crime scene fingerprint circumstantial evidence of the suspect's guilt. This doesn't necessarily make this evidence weak; on the contrary, unless the safecracking suspect can convincingly explain his presence at the burglary scene, he will be convicted. Circumstantial evidence in the form of physical clues and scientific analysis is, at least in theory, more reliable than such direct evidence as eyewitness identification, confessions, and the testimony of jailhouse informants.