Another guest that was lurking, who has decided to join up.
Does anyone have a link for this footage?
This kind of looks like the top of the septic tank, but it could just be a pile of rubble.
http://i.dailymail.co.uk/i/pix/2015/01/21/24E3D88500000578-2919401-image-m-15_1421813025453.jpg
I am wondering if the septic is a waste water treatment system. These have a number of joined tanks underground. The lid that is above ground, would be for the tank that contains the treated water, that gets pumped out onto the garden when there is enough water in the tank. (if working properly, this tank doesn't smell, hence why the lid is exposed). The other tanks would contain the solid waste and sludge, and to access these, one has to dig down a bit, as the dirt helps contain the smell.
If it is indeed a waste water treatment system - these typically have to be serviced every 3 months. (council regulations). The lid is taken off and a sample of water is taken and tested, other things are checked, and a copy of the report is sent off to council. Since it has been 4 months, one would assume it has been serviced at least once during this time.
Also, if the lid had been damaged, then it would have been replaced. (service person would have ensured it was, due to safety reasons, plus being a rental, surely the property manager would have inspected it in the 12 months since it was driven on and damaged). I can't imagine how broken bits of concrete can remain on top, without falling into the tank, unless there was an unbroken lid underneath.
The pile of bricks might just be used for them to rest the lid on when it's taken off (the lids are made of concrete and are extremely heavy - ours is in 2 halves and to remove them, we slide them off. Half a lid can easily fall down into the tank. (and what a massive pain to retrieve!)
Perhaps it had just been serviced, and something wasn't quite right, hence why the police were very interested in it when they arrived?