“My guess is money was missing.... ...”
The thing about money is you try to recover it. If you’re starting move is to shoot the guy, then throw him in the trunk without actually killing him, it could mean they were going to question him. But if that’s the plan, shooting him is high risk for two reasons. One, he knows there’s no out so why would he talk? And two, you’d have to be a crack shot and know anatomy well enough not to have him bleed out or die from shock. I’m guessing money was not the issue.
It’s something personal, in which case why bring along someone else? Or it’s political. Sixty something seems a bit old to be a spy, but in many cultures the power that comes with the job is not something you give up until you die. They wouldn’t be the first spies to turn their insider knowledge or contacts into personal money.
Since the victim was the Company Secretary, it may have been over embezzlement of funds. If the funds were spent on gambling, hookers or comestibles, or just plain wasted, then there won’t be any recovery of funds.............