Former US attorney Stanley Twardy said Tuesday that he will release a report on his investigation into possible wrongdoing involving political fund-raising and Connecticut House Speaker Chris Donovan’s campaign for the Fifth Congressional District seat. Twardy said he plans to make the report public at a press conference Thursday at the office of his law firm in Hartford. In May, federal authorities arrested Donovan’s former campaign finance director, Robert Braddock, charging him with conspiring to hide the source of $20,000 in campaign contributions. The money was connected to legislation that would have raised state taxes on ‘‘roll your own’’ smoke shop owners. Braddock’s lawyer has said that his client is innocent. Donovan’s campaign hired Twardy to investigate the allegations following Braddock’s arrest.