When it is possible to locate/trace SMS sender?

Question

I have read this question (which is closed) and already answered.

Quoting the answer:

There is no location transmitted within a normal SMS message (unless added by the author) so as the recipient of an SMS you won't normally be able to determine the location of the sender.

The location of a cell phone can be determined with varying precision by the Mobile Network Operator and any third parties with access to the MNO's system or data. The location precision depends on the capabilities of the device, the cell tower(s) it connects to and the quality of the signal.

So this makes the answer to the question HOW to locate the sender.

But lets say that the attacker goes to an unknown location with his turned off cell phone, inserts the prepaid SIM card in, turns the device on an sends an SMS message or a call with is (something illegal) i.e. death threat. He delivers the message, removes the SIM card and turn off the cell phone.

My question using the quoted answer: When can they trace him?

1. Do they need to detect his registration to the mobile network tower as he turn his mobile phone on?
2. Or is it enough that he logged in to the mobile network and left enough data to analyze it later do determine where he was.

Answer 1

Triangulation.

All that's needed is for them to be connected to the mobile network.

The mobile network operators can look at the signal of the phone to a cell tower (which is stored in records) to determine the distance of the phone to the cell tower. If it's connected to three or more cell towers, they can get a location of the phone accurate to an area of about 3/4 square mile.

The accuracy of the location depends on some factors such as how many cell towers are in the area the technology the operator uses. If the cell towers are positioned close to the phone, the resulting location will be more accurate than the phone being located far from the cell towers.