Obviously it doesn't because it means allowing the innocent to be jailed without trial, not OK.

It is not obvious. The government has an interest in being able to detain serial killers pending trial.

Yes, it is obvious that allowing the government to jail people an undetermined amount of time before a trial is defacto punishing without trial and unethical. Even "alleged" serial killers deserve a speedy trial because they aren't guilty until proven so. Rights aren't about the governments interest, they're about ours, and allowing detention without trial for years at a time is wrong under all scenarios.

I already agreed that detention pre-trial is OK if and only if there is a speedy trial.

and the principle means effective imprisonment doesn't require a trial.