Section 84: Never Works in Practice?

Okay guys, 2020 AILET PG question - Section 84 IPC - mental incapacity - now, I know this is a tricky subject. The question was: 'Rakesh, a mentally unstable person, shoots his wife in a fit of rage.' Now, the defence here would be that Rakesh was insane at the time of committing the crime due to his mental state.

But, and this is the catch, he had already been declared a lunatic by a court, but he was allowed on bail, and his treatment was going on. So, the real question is - was he insane at the time of the incident, considering the fact that he knew the consequences of his action? It's all about proving the mens rea - did he know what he was doing, and did he understand the nature and the consequences of his actions?