Hazmat crews were called to the State Capitol in Hartford after an envelope containing a white substance was sent to the building Monday afternoon.
The incident started after a member of the Governor's security detail opened a letter with an unknown substance just after 2 p.m.
Officials from Connecticut Department of Energy & Environmental Protection and Capitol police are on the scene; however, the Connecticut State Police Major Crimes Division is leading the investigation.
The area was contained and no one had to be evacuated, according to capitol police.
It is unclear what the substance is, but samples have been sent to a laboratory for testing.
Rooms 414 and 416, which are part of the governor's office, were quarantined off Monday evening as a precaution.
On Feb. 19, the mail room at the Legislative Office Building in Hartford was shut down for a few days after a letter with an unknown substance inside was sent to the governor's office.
The substance, which has not been identified, was not determined to be dangerous, even though it was sent in a letter that said it was anthrax.
An East Hartford man is accused of sending the first letter and police are pursuing charges against him.
No other details on Monday's incident have been released.
Stay with Eyewitness News for more information as it becomes available.
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