Steven Wilson, 36, sued the Ministry of Justice (MoJ) after he was struck multiple times with a nine-inch knife by a fellow prisoner.
Kyrees Sullivan, 16, and Harvey Evans, 15, died on the evening of May 22 last year when they crashed on an e-bike in Ely, Cardiff.
Emergency services were called to the A66 between Scotch Corner and Greta Bridge at around 11.45am, following reports of a two-vehicle collision.
Vladimir Kara-Murza was released in August as part of the most extensive prisoner swap with Russia since the Cold War.
The killer, who cannot be identified due to his age, admitted the murder of Tom Ellis and will be aged 30 before he can apply for parole.