Answer:
There is a saying that many in the U.S. know and use, "Innocent until proven guilty". Even if everybody is certain that the perpetrator was the defense, if there is not enough information, the person cannot be justifiably by facts be placed in confinement. After all, as Benjamin Franklin, one of our founding fathers have said,
"...[B]etter 100 guilty Persons should escape than that one innocent person should suffer...".
To keep that "one innocent person from suffering", we must be able to bring enough facts to justifiably confine a person, and not to suffer a innocent man from a harmful experience.