Mexico City, October 17 (RHC-NNN) -- Mystery deepens over the fate of 15 students who disappeared last month after clashes with police in the town of Iguala in Mexico. Vigilantes and volunteers found new, freshly-dug graves on Thursday, some with human remains in them, bringing to 19 the total number of graves found so far.

Meanwhile, the number of arrests topped 50, many of them policemen. Despite the grave discoveries and arrests, the whereabouts of the 43 students remains a mystery.

The latest burial pits were found by members of a group of vigilantes who had travelled to Iguala to help with the search. They said they had found six pits, two of which looked freshly dug but had not been used yet.

They searched three of the remaining four and said they found what looked like human remains, clothes and hair in two of them. It is also not clear how long ago the graves may have been dug and by whom.