Under Fed. R. Evid. 803(8), a public agency’s investigatory report, such as a police department’s accident report, is admissible despite the Hearsay Rule to the extent that it sets forth the investigating officer’s observations and knowledge, but insofar as it records statements by accident witnesses, there is an additional hearsay layer requiring an additional exception to be admissible. Rule 803(8) generally does not pave the way for official records to prove conclusions resting on statements by outsiders or to prove what such outsider statements themselves assert unless the outsider’s statement itself fits an exception. Factual findings, such as the policeman’s conclusions as to the manner in which a traffic accident occurred are also admissible if based if based on the officer’s factual investigation and if the rule’s trustworthiness requirement is satisfied. Here, plaintiff challenged the trustworthiness of the police officer’s conclusions and defendant never sought to show they were trustworthy. Hence, the opinions were excludable hearsay. Those conclusions were not admissible to cross-examine plaintiff’s expert since Fed. R. Evid. 705 allows cross-examination only on the underlying facts or data on which an expert’s opinion is based, not the opinions of others on which the expert’s opinion is not based. The fact that the testifying expert, had read the police report did not provide sufficient grounds, without more, to cross-examine him about its competing conclusions. The error in allowing defendant to cross-examine plaintiff’s expert on the accident report’s conclusions was prejudicial as it put the state’s imprimatur on those untrustworthy opinions and because defendant featured them prominently in closing argument.