I think therefore I arrest?

The Home Office has recently released statistics on arrests under anti-terrorism legislation between 2001 and 2008. This shows that there were 1,471 such arrests. with just over one-third of those arrested ending up being charged. This in itself would be a worrying statistic for me, but the real kick in the teeth is that the report says that this is "broadly similar to the rate for all indictable offences". So it would seem that around two out of every three people arrested by the police for the more serious offences are subsequently released without charge - am I the only one to think that this is nothing short of scandalous? The rules are (or certainly were when I studied the law) that the police have to base an arrest on "reasonable suspicion", and if two out of every three arrestees subsequently walk, that really calls into question just how reasonable - and the word means governed by reason or sound thinking - the police are being.