Peter also chose the people closest to the targets to do the poisoning. After the deed was done, they disappeared. Peter arranged for all these.
Actually, the police were already looking for these people who had disappeared in suspicious circumstances. It was just that Peter was well-prepared. The police couldn't find these people in a short period of time. Naturally, the case also fell into a deadlock, and the case could not progress for a long time.
Later, with Walter's confession, he told them everything he knew. The whereabouts of these poisoners were very clear.
To their surprise, Peter was really generous and shrewd. He directly arranged for these poisonous to go abroad so that the Chinese government couldn't reach them. Furthermore, it would take time for them to be extradited. There would be some procedures to go through.