I believe you are correct that police are the ones that investigate
and Burke is giving himself the credit. Prosecutors also aren't
typically assigned a case until there is something to prosecute.
Burke was given the Joan Webster case before there was any known crime
in February 1982. That took place in a meeting called by the Websters
after they got an anonymous call implicating Paradiso in the Iannuzzi
murder and the Joan Webster disappearance. Days later, 3-5-1982, a
grand jury was convened as the Commonwealth vs. Leonard Paradiso. It
didn't become a John Doe case until later because the testimony would
have likely gained an indictment against David Doyle for the Iannuzzi
murder. The anonymous caller had to have known Paradiso had been a
suspect in the Iannuzzi case. The caller was later identified by Tim
Burke as Patty Bono. She later made allegations in testimony without
any verification. The target was Paradiso and this was all to set up
a scapegoat for Joan Webster.
It's fair to look at the Webster background. They publically support
Burke's allegations and say they believe Bond's statement even after
it was known to be false. What convinced them? These are people well
educated, have a unique background that is by definition a profession
that digs out information, and they were involved in the
investigation. Was Burke or law enforcement so convincing the
Websters were deceived? Why would they deceive them?