To improve inferences about psychological and social evidence contained in pictures and texts, a five-step algorithm—Systematic Analysis (SA)—was devised. It combines basic principles of interpretation in forensic science, providing a comprehensive record of signs of evidence. Criminal justice professionals evaluated the usefulness of SA. Effects of applying SA were tested experimentally with 41 subjects, compared to 39 subjects observing naturally (naturalistic observation) and 47 subjects guessing intuitively intuitive guessing group. After being trained in SA, prosecutors and police detectives (N = 217) attributed it a good usefulness for criminal investigation. Subjects (graduate students) using SA found significantly more details about four test cases than those observing naturally (Cohen’s d = 0.58). Subjects who learned SA well abducted significantly better hypotheses than those who observed naturally or who guessed intuitively. Internal validity of SA was a = 0.74. Applying SA improved observation significantly and reduced confirmation bias.