CLEAN : Forensics on scene after police arrest knifeman near Parliament

The video describes a quick incident where an area was sealed off. A man was seen on the ground, and individuals were detained by police officers who appeared calm. Despite the calm demeanor, there was a tense atmosphere as firearms officers were running, indicating something significant had occurred.

What can be inferred about the atmosphere during the incident?

How did the witnesses perceive the situation at the time?