Ben Carson, the neurosurgeon and Republican presidential candidate who has condemned Planned Parenthood’s donations of fetal tissue, once carried out research on tissue from aborted fetuses.

Jen Gunter, an OB/GYN and science writer, put on her blog Wednesday night a study co-authored by Carson in 1992 that used tissue from two fetuses aborted at nine and seventeen weeks, according to the paper.

But in the wake of hidden-camera videos alleging that Planned Parenthood illegally sold fetal tissue to researchers, Carson told CNN that the organization “doesn’t seem to understand the sanctity of human life and is willing to destroy that” and “virtually everything that can be attributed to progress by using fetal tissue can also use other types of tissue.”

Carson denies any contradiction between his stance on Planned Parenthood and his former research. He told Buzzfeed, “Killing babies and harvesting tissue for sale is very different than taking a dead specimen and keeping a record of it, which is exactly the source of the tissue used in our research.”

Planned Parenthood admitted donating fetal tissue to researchers but has denied seeking payment beyond legal reimbursement for its costs.

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Write to Tessa Berenson at tessa.berenson@time.com.