Nobody said there IS an ME finding or declaration of death. All that was said is that 'police believe', based on the preponderance of evidence which they have pieced together into what they feel is a 'whole' picture, which they say is enough to believe the trio are dead and the murderer is DG.
It is rare for a murder trial to have no bodies, but that is an extra burden of proof that LE/prosecution will have to prove in order for DG to be convicted by a jury. I believe that death certificates are public, are you able to provide one to say they exist for the three?
In the tragic case of Ontario's Tim Bosma, he remains were unidentifiable, and I am not certain there was any ability to extract any DNA from those remains, but even so, those remains were handed over to the family for proper burial. If there were enough 'remains' to prove death and allow an ME to make a declaration of death, those 'remains' also would have been handed over to the L/O families. But they weren't. Because they don't exist. And if an ME had made such a declaration, the Chief would have instead stated, 'the trio are dead based on the ME report'. It is that simple. But that was not done. The fact that the Chief, after making his well written statement of 'belief', then responded to a media's question, by stating 'they are dead', is still only his opinion. LE's opinion, perhaps also obviously the Crown's opinion, but still not deemed enough evidence to proceed to trial, that will be determined next spring, I believe. When that happens, assuming the charges against DG can proceed to trial, DG will be given his 'day in court' (which will of course actually be months, undoubtedly). It will then be the burden of the prosecution to prove to the jury beyond reasonable doubt, that not only is the trio dead, but also that DG is guilty. These things are simply not fact until then.
It IS possible to charge someone with a homicide without a death certificate.