Capitol Police are investigating an incident Wednesday in which the Gay Pride flag that hangs outside of California Democratic Rep. Alan Lowenthal’s office was thrown to the ground and stomped on.

Staff was told by witnesses that the perpetrator was a man who appeared to have been a visitor to the Cannon House Office Building with what appeared to be his wife and young son. The incident occurred on Wednesday.

Yesterday, a man threw #PrideFlag outside my DC office 2 floor-stomped on it-called it disgusting & immoral. We must pass the #EqualityAct!

— Rep. Alan Lowenthal (@RepLowenthal) March 16, 2017

The flag was not damaged and placed back where it hung opposite a U.S. flag on either side of Lowenthal’s office door.

Lowenthal’s office said staffers were told by Capitol Police that they were investigating the incident and trying to identify the man. A spokeswoman for the USCP told Roll Call it does not  comment on ongoing investigations.

The flag has been outside of his Cannon office since March 2013 and was the first Pride Flag to fly outside a Congressional office on a permanent basis, the House Historian told Lowenthal’s office.