Residents of Winthrop House were surprised to find their Junior Common Room locked and the entrance covered with police tape on Sunday.

Early that morning, officers of the Harvard University Police Department (HUPD) found the room covered in white dust after a fire extinguisher was shot off, said HUPD spokesperson Steven Catalano.

"Environmental Health and Services closed the room off to clean it up," Catalano said.

He said that there is an ongoing investigation that HUPD is taking very seriously.

"We are looking at this as vandalism," Catalano said. "Call it a prank but it is going to take a lot of effort to clean up. There was a white chemical residue all over the room."

Assistant to the Winthrop House Masters Karen Reiber sent out an e-mail message yesterday to residents of the house concerning the room.

"As many of you know, the JCR is not currently available for use, nor do we know when it will be cleaned up and available again," Reiber wrote.

The incident is the latest in a string of vandalisms which have plagued Winthrop House recently, including broken chairs, ripped window screens, and damage done to the frame of a portrait of Thomas Hollis which hangs in the dining hall.

On March 12 Co-Master Paul D. Hanson sent an e-mail to Winthrop residents threatening to close the dining hall, which is currently open 24 hours a day with access to drinks, if the vandalism did not stop.

"The vandalism involved is a wanton attack on the quality of life of all residents of John Winthrop House, " Hanson wrote. "It simply strikes us as incomprehensible that anyone could willfully damage irreplaceable art."

Hanson declined to comment on the incident, citing the current police investigation.