Well from what I remember "Lucky" Lochlan (why does he have the nickname lucky when he is anything but?) is out of the frame as far as we know, when asked who knew the safe's security code Chrissy's answer was just her Lawrence and Robert. Although one other person who might know is Nicola (although she is abroad); and of course with the way Lucky creeps up on people it is always possible that he has found it out, but then how did Aaron get the gun?
Other possibilities are:
Pollard:Have his schemings gone a step further than anyone has thought?
Jay Sharma: There is nothing at all to connect him that I know of at the moment, but he is a very loose cannon at the moment.
Also knowing the way that the script rolls it could be someone that has not made an appearance yet - a "hired gun".
Everything seem to point to Aaron at the moment though with him having a gun!!
Corrie
On a similar vein do any of you watch Corrie? About a week before he died I noticed something unexpected about Callum (the drug dealer). With his life style: loads of money and bling, why was he wearing what looked to me like a bog-standard off the shelf Casio watch? I noticed as I was watching on my laptop (and therefore closer to the screen than usual) when he was in his car and burying his head in his hands gave a close up of his watch.
Was this something that was overlooked by the continuity team (although I have no idea what watch he wore previously, it does seem a little out of character for someone who has "loadsamoney" to use something like that.