What would be the reasoning?

I have a story idea for a crime thriller. I have everything thought out for the most part except for this one part. So it's about a group of criminals that were planning a huge heist in Columbus. However, the cops find them all murdered in a house just a few hours before the heist was supposed to take place. Now, this is where I struggle. What would be a reason, not too predictable, that all these people would be killed? If you have any ideas please help, I'm stupid and can't think that far.

 

One person thought another person was going to betray them and things went badly.

 

The explosive/gas/poison they were going to use for the heist went off - either by itself or somebody set it off by mistake or with intention.

 

Another group of baddies was planning the same heist and didn't want the competition.

 

Vigilante found out about it and got to them first

 

That's an interesting idea. So there is a vigilante loose, bringing down criminals? That will give the police something to do, for sure.

 

It was all a decoy for their real plan of breaking into the new high-security crime lab with automatic defence systems. All evidence in the laser protected vault would be destroyed to cover their tracks from previous assasinations. One of them was still alive using medicine slowing down the heart rate. The others were dressed up beggars that were killed after generously cleaning and shaving them. The dead bodies contained high-tech equipment needed to break into the vault.

 

Damn good!

 

Precogs

 

Ok... I tell this to you but you must keep the secret.

I am the original master mind behind this. I found a way to do heists by fooling criminals.

First I must find someone who thinks he is the mastermind. And he must be well connected. And I must know what those connections are.

I tell him about this huge heist which I will do if I can get funding + connections. He thinks that I'm fool because I tell him, because I don't have resources and because he thinks he's smarter than he is.

So... He steals my plan because he thinks he can fool me.

And then I follow him secretly. And I let him do all the heavy lifting.

When he has all the resources ready, I come and rob it. But you know... They would not let me and they would come after me and... So... I must take care that things go silent and passive.

So... The real heist is me robbing criminals who thing they are robbing my plan and doing the big one so they can retire. And... In a way... They will retire.

But remember. Don't tell this anyone.

 

The place they were planning to hit was mob-connected, somebody talked,