There was criminal intent , at the very least , to cause serious injury and there could have been proven criminal intent to kill or he wouldn't have been charged with murder . The CPS must have had enough evidence to charge him with the murder of the victim but the court decided he was guilty of manslaughter, not murder . However this is a very thin line and the reason why people convicted of manslaughter often get very heavy sentences .
Its one step down from murder , the copper would have known what he was doing was going to cause the victim serious injury
That would have been ABH , GBH etc if the victim hadn't died
Clearly the manslaughter verdict is the right one