I believe that Alistair was always meant to be murdered and that people are concentrating far to much on the envelope and why he would be allowed back in if it was a hit. This inturn is distracting them from trying to make sense of it and the more you read, the more confused you become. I know that's what happened to me for a while.
I do believe it was a murder for hire plot arranged by someone he had upset ( finances) possible an affair, and the person who arranged it either knew violent gang members, or had a violent friend.
When a murder for hire is arranged by a third party 9 times out of 10 you find that the person who is requesting the killing usually provides the weapon.
In order to give you some context. There was a murder of a off duty police officer called Nisha Patel- Nasri. Her husband had hired someone to kill her and had given the killer keys to his house to do so while he was out. The hired hit then used a knife from their knife block, killing her inside her house. 10 days later just like in this case the knife was found down a drain a few streets away, just outside the search parameters.
The reason for dumping the weopan in this way is because they know that it will not be traced back to them, and they don't want to be walking around with it on their person after the murder. Especially when the police & paramedics are likely on their way. ( in this case very close by)
They then walk away usually in the direction of waiting vehicle In this case on the dimly lit links carpark with no CCTV, where coincidently tracker dogs did follow a scent to ( Perhaps to the same 4x4 Mitshibishi seen the night before, and they disappear. ( likley to Inverness)
With that in mind and knowing that the small calibre weapon he had been provided with meant he needed to be close to his target in order to kill him, perhaps that's why he used the envelope. ( Alistair handing it back insured that closness.)
The man who initially knocked on the door with the envelope likely gave him a




-and-bull-story about what was in it, ( hence his bewilderment) so when he went back inside to look and found it to be empty, and that it was not addressed to him, he obviously went out to check if the man was still there. (Matching what we the public know).
If we remember what Veronica said to Journalist interviewing her. "His decision to go back and see if he was still there was based on what the killer had said"! Now it makes more sense.
However by the time Alistair returned it was a different man standing there, not the guy who handed him the envelope. And that is who shot him.
Veronica only saw the back of him walking away, and let's say, in a bid to turn a profit the people who made the Blouson jacket and the Cap the man she saw was wearing, made more than one, and the two people involved wore the same/simular outfits.
Perhaps the envelope really had contained nothing, but initially it had contained the gun, and Paul was who it was delivered to, and Paul's acomplice had just reused that same envelope. ( explaining why his name was on it).
I have also read that in the early hours of Sunday morning neighbours reported seeing a 4x4 Mitsubishi parked up outside Alistair’s house, and that the men inisde were acting suspiciously, and after being disturbed, they drove off. That being the case perhaps that was the same vehicle waiting for the killer on the links carpark.
Maybe the way to solve this crime lies further back in Alistair’s finances before he moved to Nairn, and lies in how he financed Lothian House.
That was a 9 bedroom property, with 6 bathrooms and 3 reception rooms. How does a 28 year old man finance something like that? Speaking to the chartered accountant who was involved with that purchase would likely uncover any unusual transactions.
When he was seen gambling what was described as large amounts of money 2 days before his murder, still in his suit, going there straight from work. Was he laundering money through the bookmakers, rather than through the bank, which is why police found no unusual transactions at the bank?
Looking at the fact he could afford to take a job with a lower wage, gamble large amounts of money and still afford to run that property, you have to question where his finances were coming from.
Had the closure of the B&B buisness he had initially bought Lothian House for the purpose of, caused the problem? Rather than his decision to leave the bank?
The intent was always to kill Alistair imo, and the motive could be anything some one will eventuly guess right, but perhaps trying to find that 4x4 Mitsubishi seen the night before might be the way to go. My guess would be one of the men seen in it was named Paul.