TIXTLA, Mexico (AP) — Mexican police sent horse-mounted patrols and officers with trained dogs up into the hills around the city of Iguala on Wednesday in an expanded search for 43 college students missing since a clash with police last month.

The stepped-up hunt was ordered after investigators determined that 28 sets of human remains recovered from a mass grave discovered outside Iguala last weekend were not those of any of the youths who haven’t been seen since being confronted by police in that city Sept. 26.

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