All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Public pools are places set for swimming and whoever works there should adhere to the conditions and regulations that guarantee the safety of all swimmers and visitors.
Offering Diyah(Blood-Money) and Kafaarah(Expiation) is obligatory in case of accidental or intentional killing when the guardians of the killed spare the life of the killer from Qisas(Retribution). They are also obligatory when a person causes the death of another. In all these cases, either the victim was killed intentionally, unintentionally or someonecaused his/her death. However, in case there was no act or cause leading to the victim`s death, neither Diyah nor Kafaarah is due.
Accordingly, as understood from the above question, and as the court found the questioner not guilty because he wasn`t negligent, no Diyah or Kafaarah is due on him for he didn`t commit any act leading to the victim`s death, neither by initiation nor by causing. And Allah knows best.