Military abductions (MILABS) have reportedly been conducted on alien abductees to learn what happened to them, or as part of a CIA mind control program. According to the UFO Encyclopedia(1), such abductions may also indicate the U.S. military is cooperating with aliens in their monitoring of humans. For more, see this article(2) by Helmet Lammer Ph.D.

1. http://www.amazon.com/exec/obidos/ASIN/0743466748/ctoc
2. http://www.alienjigsaw.com/yk2/milab.html