if "they" refers to the prosecution: well, i sure hope that the prosecution believes he is guilty before a trial starts. i think the alternative is that the prosecution prosecutes people at random?

if "they" refers to the judge: definitely not. seizures like this are because they have evidence against him and have what the judge believes to be a reasonable case; this does not mean the judge believes the defendant to be guilty. maybe you don't think the case is reasonable, and maybe its not, but its a far cry from "guilty until proven innocent"