To think my sister wouldn’t steal from my mum?

[MuggyMcMuffin]

My mum called me this evening in a state. She’s an older lady who keeps envelopes of money in her house and knows the exact spots for each envelope. She usually withdraws money from her bank and then shares it across the envelopes. This evening, she went to add some money to a certain envelope only to find that the envelope was gone. It had around £2.2k in. I went round to check for her and it’s definitely not there. She last added money to it 2 weeks ago.

Mum had told me that years ago, my sister had stolen from her on 3 occasions. She has suspicions that my sister has stolen the envelope. My sister is often at mums house before going to work.

AIBU to think my sister wouldn’t do this?!

get the family together and explain - the money has gone missing can we all have a good look round mums house and if doesn’t turn up we will need to get police involved as it’s obviously been stolen - no accusations made but will be putting everyone in the picture and can see their reactions. Hope it turns up

My mum, who is now 90, caught her sister stealing money from their mum over 40yrs ago. Mums sister didnt think it was that big a deal..Their mum couldn't understand where her cash was disappearing to.
My mum never spoke to her sister again. Their mum died not long after after suffering a massive stroke. Her funeral was the last time my mum saw her sister, who has now also died.