The owners of the site where Ana Kriegel was murdered were told by a local authority it was being trespassed on and might end up being used by rough sleepers.
Fingal County Council raised security issues over Glenwood House in Lucan, Co Dublin.
The 14-year-old girl was killed at the site, which now has planning permission for a care home, in May 2018.
Officials were concerned it would be used in the run-up to Halloween to find material for bonfires.
In correspondence with the owners’ representatives last month, the local authority said they had carried out an inspection and discovered a damaged fence at Laraghcon, Clonee Road.
One email said: “The site can now be accessed by pulling this fence aside.
“There appeared to be signs of trespass also within the site.”
The council also warned of other access points including a back entrance to the farmyard.
An email said: “It is easy to walk up the bank and around the fence to gain entrance to the site. This definitely needs to be secured.”
Another email added: “Consideration should be made to close up the doorways to these outhouses as they could provide a shelter for people sleeping rough.”
Two other possible access points were also flagged including a rotten window and a fence at the front.
Temporary corrugated metal sheeted roof had been installed to make the shell of the protected structure “weather tight”.
