The detail's of Rusty's demise (and the story behind the identification of his then unmarked grave), is given in the excellent book 'The Greatest Squadron of them All' (by David Ross, Bruce Blanche and William Simpson). Page 236 in Vol 1 states that the Squadron records give his loss as between 09.34 and 10.34 hours. It unfortunately does not give any details regarding the exact foe other than 'combat with II/JG26 over Biggin Hill at 10.00 in Spitfire X4261. Given that Von Werra was from II/JG3 it may seem unlikely it was he who shot down Rusty.
However, Von Werra's unit was initially attacked by 41 Sqn and 'Stap-me' Stapleton caught up with a single 109 (Von Werra's) forcing it down at Love's Farm, Marden at 10.10 hrs. Again the Squadron's F540 recording Stap-me's combat report at the same time as the report of Rusty's loss, between 09.34 and 10.34.
Still no clearer I suppose?