There was a party going on. At some point, one of the guests felt ill. When the investigation had taken place, it was discovered that the guest had been poisoned. He's going to make a full recovery, though. When the speculations began, Jake said that he knows a person who had done it. When he reveled who that was it confirmed suspicions of the police. Everybody then asked how did you know he was the one who had poisoned him?

Correct it if you can, please. And explain why it's wrong as well. Thanks.
Popraw to, jeżeli możesz, proszę. I wyjaśnij też dlaczego to jest to źle. Dzięki.

Question

There was a party going on. At some point, one of the guests felt ill. When the investigation had taken place, it was discovered that the guest had been poisoned. He's going to make a full recovery, though. When the speculations began, Jake said that he knows a person who had done it. When he reveled who that was it confirmed suspicions of the police. Everybody then asked how did you know he was the one who had poisoned him?

Correct it if you can, please. And explain why it's wrong as well. Thanks.
Popraw to, jeżeli możesz, proszę. I wyjaśnij też dlaczego to jest to źle. Dzięki.