Leo Crow essentially commits suicide in the movie. This is contrary to what the pre-cogs predicted, but it is a death of passion. If Agatha had been in the temple, would the pre-cogs have created a brown ball for this passionate death, which was essentially self inflicted?
No, they don't detect suicides.
From the original script by Scott Frank
ANDERTON : The Precogs don't see what you intend to do, only what you will do.
WITWER : Then why can't they see rapes, or assaults... or suicides?
FLETCHER : Because of the nature of murder.