You seem to be missing the point. Police aren't obligated to tell us what evidence they have, but there is also no reason for them to be misleading us with vague implications that they possess evidence that they (possibly) do not actually possess. If they choose to speak to the media about certain pieces of evidence, then they should be more clear and straightforward with their statements.
Not at all. Police have made a press release that provides the public with assurances that the perpetrator, Luka Magnotta, has been apprehended and that they have sufficient evidence to not only have him extradicted to Canada, but to prosecute him for first degree murder. Police have no obligation to provide any more information.