A Suffolk Superior Court judge has refused to order separate trials for former state probation commissioner John J. O’Brien and his codefendant, ex-Treasury aide Scott S. Campbell — even though lawyers for the men argue a single trial will pit the two against each other.

“The blatant finger pointing by the defendants will deprive O’Brien of his right to a fair trial and contravene the best interests of justice,” wrote O’Brien’s lawyers, Paul Flavin and Brendan Pitts.