That only says 'at' the house, rather than in it, seeing as the alleyway joins onto the house as far as I can tell, that doesn't really clear it up.
Just seems odd to me to cordon off an entire alleyway if the body was inside the house - it would also beg the question of how they would have just randomly got a tip off about her being in the house, whereas someone walking down the alley may have seen/smelt something.
http://www.bbc.co.uk/news/uk-england-london-19214964
Police searching for the missing schoolgirl Tia Sharp have found a body in her grandmother's south London home.