They had from Monday evening to Friday afternoon. With the number of forensic people on site and the ability to expedite forensic results if needed they had plenty of time to test and associate him with the crime.
It does seem fast but they had access to the owners, management agents, neighbours and estate agents. All that plus any forensic evidence they found at the scene.
In my mind it's obvious they have enough to make such a strong statement.
I also come back to the "no danger to the public" comments on Monday or Tuesday, perhaps there was something very clear pointing to him which made this statement possible... again that is speculation but seems like a reasonable one to me at least.