Hardeep Singh Nijjar is expendable to nearly every government in the world. No government will sacrifice their relationship with India for a Sikh nationalist, even Canada. This situation is just like the Adnan Khashoggi killing by the Saudi's. Sure, the USA press raised a stink and USA politicians had to scold Mohammed Bin Salmon. But, like India, Saudi Arabia is too needed to banish. Canada will, after a year at the most, look the other way and resume normal relations with India.
there is intelligence. there is legal evidence in court of law. I suspect there is intel but not enough legal evidence for a law enforcement.