Several companies, developers and properties have been linked to a federal investigation surrounding the Contra Costa County Assessor’s Office, according to grand jury subpoenas made public earlier this week. A closer look at the records shows that prosecutors are examining some of the county’s biggest taxpayers and most prominent builders.

The subpoenas — obtained by the Bay Area News Group under a California Public Records Act request — seek documents including Martinez Refining Co., developers responsible for the construction of tens of thousands of homes across Northern California and several…