Illinois Supreme Court Rule 236, titled "Admission of Business Records in Evidence," sets forth the foundation that must be established to use business records as substantive evidence at trial. Subsection (b), however, specifically states that police reports are not admissible as business records--
Although police accident reports may otherwise be admissible in evidence under the law, subsection (a) of this rule does not allow such writings to be admitted as a record or memorandum made in the regular course of business.
As Rule 236(b) makes clear, while you cannot escape the effect of the hearsay rule by establishing a police report as a business record, there might be other ways to get the evidence admitted. For example, diagrams are not rendered inadmissible just because they are part of a police report. By laying the foundation necessary for demonstrative evidence, you might be able to use the diagram apart from the report. See, e.g. , Hargrove v. Neuner, 485 N.E.2d 2 1355 (5th Dist. 1985).