As I stated earlier, he didn't have to mention the 'who's' or the 'hows' or the 'wheres' or the 'whys', but a simply statement saying that the ME has provided irrefutable proof that the victims are deceased, would have been informative, and not risky to the accused, or the case, or the trial, if it were in fact true.
Just to add to news.talk's comment -
Say, for example, Chief Hanson was more revealing of details, and he said "we base the determination that the 3 missing are deceased on the following: DNA testing proved that the massive volume of blood found in the L home belonged to the 3 victims, and was so voluminous as to be incompatible with life" IMO, this is too much information, and it could be argued to be inflammatory or sensational, or an impediment to the accused's right to a fair trial. It's possible the determination was based on even more gruesome evidence - such as brain matter, or traces of other vital organs, or evidence of dismemberment. imo, defence counsel would cry foul if that degree of detail was revealed.
Just speaking for myself, I did not need to hear that degree of detail from Chief Hanson in order to believe the Ls and NO are dead.
JMO