Charges dropped against executives in corporate kickback scandal

R v Carter and R v Georgiou - talk about a disaster of a case!

The Crown no billed a 13 week criminal trial in the first week after it came out in evidence from one of the lead detectives that the Police:

(1) had not disclosed the existence of a registered informant to the defence;
(2) had thrown away an original, signed witness statement that differed from the final witness statement filed with the brief of evidence; and
(3) relied on Orix's lawyers, Clayton Utz, to review and forward relevant evidence to them.

While I can kind of understand (2) and (3) happening, I just can't understand why you would not disclose the existence of registered informant to the defence.

https://www.smh.com.au/national/nsw/charges-dropped-against-executives-in-corporate-kickback-scandal-20190916-p52rsb.html