Anyone “might” be armed.
The arresting officer would explain the circumstances of the arrest to the custody Sgt and request a strip search or having heard the circumstances require one themselves. This request sits at a certain stage in the process, normally at the charge desk, where a wand and a searching officer are present and the arresting officer is a cover officer.
In this case, it appears that the Sgt has come into the holding cell, to carry out the Covid check and the shooting has happened prior to the more in depth search.
Would the suspect still be in cuffs in the holding cell?