http://imdb.com/title/tt0066954/

A childless middle-age couple adopt a troubled youth they find living in their crawlspace and attempt to get him to rejoin society with tragic results.

FYI: I'm requesting the 1972 movie based on the Herbert Lieberman novel of the same name, this is not a request for the 1986 film.

I did a global search and didn't come up with anything on the 1972 title---any help in locating this movie would be very much appreciated.