Because that was up stream from where they found the doll.
I gotta say, that as someone that has been very happy with the entire season so far, and has thought every episode moved along at the right pace (slow, but no different from last year), last night's ep was a disappointment. With all the secrets coming to a head, I figured we'd get a bit more out of it.
I will say I'm loving where they are taking Andrea, as well as Glenn and Maggie. I've been tired of Lori for awhile, but last night was the final straw. I get it, you aren't happy, but somehow or another Andrea is making a go of it, and has far less depending on her than you do. Get it together. I'm so tired of her whining about bringing up a kid or bringing another kid into the world! Gee, you can't have your morning latte and watch Oprah any more? Get over it. 99% of the history of humanity has been about people struggling just to survive - they managed to pull it together, there's no excuse you can't. I understand her having that conversation once, but after about the third time it starts getting old.