Board Thread:Episode Discussion/@comment-14138255-20160131163802/@comment-26397825-20160201091612

By capturing them. Yes, they die in captivity, but there'd be enough time before they die to get at least one or two experiments in. It'd be very dangerous though.

Also, observation, and Huntsmen probably have a passive mission to report on anything unusual about any Grimm they fight immediately upon returning home.