I am only noticing this now, after who knows how many rereads I gave this, but... Kishiro-sensei doesn't go low on details, the cell where Alita is being kept clearly is made to keep dangerous and powerful prisoners for questioning, and it has seen some action in its life.
There are dents and scorch marks all over, even the bulletproof table where the guy is seated has dealt with a lot of punishment, probably because of how it is constructed, if you look at it... the turrets right behind Alita must be some sort of plasma burners (as it is the form of energy most useful even against high-level cyborg) and the way the side "walls" are positioned it forces the plasma to go directly to the table.
Not only they must have burned a lot of prisoners on that when they get rowdy, there is a chance some even escaped and caused some mayhem before being taken down.