Whenever I've heard of the arrest of high profile suspects , there is almost always some smart plan to get the person before they can engage in violence.
This is done to get them to cooperate and get the network that supports the high profile suspect.
I'm not sure why it went down as it did. But I know reality is complex, so I'd guess they were aiming for better but things went badly and they preferred to take him out for sure than let him get away. That would be my guess. That or someone wanted him dead, but the latter is less likely (stupidity being more common than malice and all) - There are probability other probabilities I'm not considering and the fact that multiple factors could be at play... it's hard to tell, the article was short on details.