Nous ne pouvons pas être absolument sûrs que c'est X qui a tué Y, mais nous pouvons en être assez sûrs pour que ce soit sûr !
There's obviously some amusing wordplay at work here that revolves round the use of three "sûr(s)".
I'm sure that the part in bold means "(even if we can't be 100 per cent sure), the odds are as close to 100 percent as can be", but I'm not sure of its exact meaning (more word-for-word interpretation).