He'd have a defence in Britain. He'd plead what we call "diminished responsibility". This is a defence to murder and is based, in a case like this, on the defendant losing his self- control when subject to extreme provocation. However, the defence only reduces murder to manslaughter. But the penalty for manslaughter can be anything from a fine or conditional discharge to a long term of imprisonment, whereas for murder it is only life imprisonment.
The Grand Jury serves the purpose of a magistrates court in deciding whether the prosecution have established a prima facie case, in what we call committal [for trial ] proceedings. Committal proceedings have effectively been abolished here. Now, in such cases, the defendant appears in the magistrates court and the case is immediately sent to the Crown Court. As suggested above, the function of the magistrates, in deciding whether there is a case fit to be tried, is now performed by the CPS