LOS ANGELES — Robert Durst was a rich man living free despite police efforts to link him to murder. Adnan Syed was a young man imprisoned for life for killing an ex-girlfriend. Media scrutiny changed their fortunes, pushing both back into the courts: Durst is facing trial on a murder charge, and Syed awaits an appeal of his conviction. Observers say it’s what journalists, or others taking on the role of investigative reporters, can and should do — but not simply, or heedlessly, to play faux …