Ask said neighbours whether they have any poop bags or scooper as there is a dog dump on your patio.
Make sure it doesn't do it again by using some sort of spray deterrent. This usually has lots of citrus in it which pooches dont like. Dogs normally sh1te in certain areas so using a spray will put the dog off sh1tt1ng there. You will need to spray this regularly for a while.
I'm a dog owner and my dog would regularly crap in the next doors neighbours garden much to my horror. I'd pick this up and dispose of it, apologise and let her know that if she ever found any to knock on my door and let me know. Luckily we get on and she likes my dog.
In the end though she put up a gate to block access as she is keen on her garden. Problem solved.
I'm sure if you let your neighbours know that this has happened they will be mortified. Simples.
Of course as you sound a bit tense you could always take the largest kitchen knife round and kill the whole family before setting fire to the property to hide your crime.