He used mocked up bank statements to 'prove' to Diana that her body guard and some of her pals were being paid to monitor her movements. Also told her that Chas was overheard plotting to have her bumped off and even claimed that a swatch watch that Chas had given William (who was then 12)was a listening device so that Chas and his band of assassins could eavesdrop on William's phone chats and conversations with Diana. He deliberately messed with a mind that was already fragile and made her even more paranoid that she already was.
I hope the people he maligned in the bank statements sue his arse off, but it would be a hard case to prove since the disc containing the original mocked up statements was stolen from the home of the beeb guy who Bashir used to compose the statements. I know that Earl Spencer made notes of a meeting with Bashir and mentions seeing the bank stuff and the guy who created it for Bashir is still around, so you never know. Earl Spencer told Diana not to get mixed up with Bashir because he was a total fantasist, but Diana being flakey just said OK ... and then promptly GOT mixed up with the liar Bashir.
Bashir is just a dirty money grabbing bastard who used a vulnerable woman to get himself a scoop,
duck him.