Why would an officer go though an intersection against the light without using their lights?

I know there are times when they respond to calls and don't want a suspect to know they are coming. I recently saw an officer make a left hand turn from the right hand lane cutting off traffic without using lights or sirens. They were responding to a collision about a mile up the road. I know this because... show more I know there are times when they respond to calls and don't want a suspect to know they are coming.

I recently saw an officer make a left hand turn from the right hand lane cutting off traffic without using lights or sirens. They were responding to a collision about a mile up the road. I know this because I was headed that direction and saw them parked in the road behind the vehicle involved with lights flashing. I was wondering why they would not turn on the lights before cutting off traffic in the intersection.
Update: tap158: If they received the call while going though the intersection, why were the making a LEFT from the RIGHT hand lane? The Boss: It is not possible to be undercover in a MARKED patrol car with lights mounted on the roof. So far, I'm leaning toward 'they forgot'. I was just wondering if I... show more tap158: If they received the call while going though the intersection, why were the making a LEFT from the RIGHT hand lane?

The Boss: It is not possible to be undercover in a MARKED patrol car with lights mounted on the roof.

So far, I'm leaning toward 'they forgot'. I was just wondering if I would get a different answer that made sense.
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