Thayer Hall returned to normalcy last week when the administration lifted the ban on guests in the dormitory, after three weeks without new incidents of vandalism.

Assistant Dean of the Summer School Michael J. Prokopow first announced the no-guest policy three weeks ago, in an effort to stop a wave of vandalism that fouled the dormitory with obscene graffiti and human waste.

The policy extended even to out-of-town guests and parents of resident students.

Prokopow declined to say yesterday whether the person or persons responsible for the numerous incidents of vandalism in Thayer had been discovered.

The dean had said last month that the guest ban would not be lifted until the vandal was held responsible, and said yesterday that, since the ban was lifted, "one can only assume that the investigation ended satisfactorily."

"Clearly, something happened," he added.

Harvard Police Chief Francis D. "Bud" Riley said yesterday that he did not think the police were involved in the search for the vandal, and that he did not know whether the perpetrator had been caught.

Summer school students reacted with little emotion to the lifting of the no-guest ban, in marked contrast to the outrage they expressed when the ban went into place.