William Blair says its a buyer of Cardiovascular Systems after the company provided an update on the previously announced letter from the Department of Justice related to an alleged violation of the False Claims Act. Despite investigating for 14 months, the Department of Justice has not yet taken action on this case, the firm tells investors. It believes the case likely lacks sufficient cause for the DOJ to pursue it. In a worst case scenario, William Blair sees the company paying a small fine up to $5M. It views Cardiovascular's valuation as compelling and is a buyer at current levels