to escape a punishment or be missed by a system that should deal with or protect you

Once again terrorists have slipped through the police net. 恐怖分子又一次逃脱了警方布下的罗网。

There are laws to protect the mentally ill, but now and then someone does slip through the net. 虽然有保护精神病患者的法律，可是时不时会有人没有被照顾到。