Because intelligence is not evidence. Knowing something is not the same as being able to prove it (and, going by the posts on numerous previous threads, unless you can prove something in a criminal court, it isn't true and doesn't exist).
If it could be done, it would be done. But unfortunately, experience over the last 25 years is that it can't. Juries will believe anything ... and with a conspiracy charge it is dead easy to claim that things have been misinterpreted.
(Example: Info received from oridinary member of public about man acting suspiciously watching Post Office cash delivery. Observation on next two weeks confirms this - nothing criminal but clearly lurking around watching how the delivery happens. No idea as to identity and suveillance fails to identify him. On third week, delivery is robbed. Interception is ordered but due to radio failure is delayed by a few seconds and getaway vehicle drives off. During pursuit shots are fired at police and police fire back (no-one hit on either side). Following chase, two suspects arrested nearby (with members of public witnessing the whole thing and confirming police account) with large handgun and bag of money. No comment made in interviews. Charged with robbery, etc. Defence get up in Court and say "We thought this was a police training exercise. We were informants (they had previous for robbery) and we thought we were just helping them out.
No evidence to corroborate this ridiculous claim. Guilty or Not guilty? Not guilty.
)
