Telephone records - Zodiac investigation

[crypto]

I watched the movie Zodiac, and it made me wonder…

How did the phone company track calls back then, and did they track calls like today?

As I understand how things work now, when I call another phone number, regardless of cell or land line, if there is a connection on the other end a record is made of the call… It shows the initiating and receiving numbers, date and times, length of call and - if it was made on a cell phone, what tower the call was made near (among other info, I’m sure).

But what about when technology was a bit more primative?

When you made a long distance call back in the 70’s, that was recorded. But as far as the billing went anyway, you paid for zones. So, you could pay for a local area that included maybe your area code, or a large number of prefixes under that area code, but these calls weren’t broken out on the bill. The only information I think the phone company would provide is the number of calls made per month.

If you went outside that local zone, but in the same city, the call was treated like a long distance call, and you saw the number and length of time.

But I have no idea what the phone company recorded on their end, or how searchable the data was (or is, assuming they still have it).

The reason I bring this up is because there are a number of calls that the Zodiac (allegedy) made, including the calls to Melvin Belli, as well as the calls to Darlene Farin’s family the night of her murder. If the Zodiac called someone today, I am sure the phone company could look at the calls that came in on the number called, and figure out what number was used to call that number based on the time of the call. But could they do that back in the 70’s, when the Zodiac was doing his thing?

For billing purposes, I am sure the call was recorded, but I don’t know if they would have been able to do a reverse search on the call like I am suggesting. If it was a local call and fell into the callers local zone, maybe no detailed record was ever created.

Anyone know? I am sure if they could have figured out where the call originated from, they would have. But since they didn’t (as far as I know), the call was never pin-pointed.

He also made calls from pay phones. But the police were able to figure out the origin of those calls, since pay phones calls created the information record I am referring to.

[Mr_Downtown]

I don’t believe there would have been any way to know about calls made to a “local” phone number: one in the same exchange or that was not a “toll call.” Law enforcement agencies could get a warrant to install a pen register that would note what numbers someone dialed (something called a trap and trace device did the same thing for noting who called in to the villain’s line).

Calls from central city to suburbs, or between widely scattered parts of a big city, were often toll calls for which a charge was made—and thus a billing record would exist. I don’t know if that was the case for calling Brooklyn from Manhattan, or vice versa.

[Francis_Vaughan]

In the time frame of the movie exchanges were still mechanical. Indeed it wasn’t until the 80’s that exchanges really started to transition to digital, and that still took quite a while in many areas.

You could trace the origin of a local phone call, whilst it was occurring, by simply getting a technician to walk through the exchange and note down the physical position of the mechanical selectors. The moment the call finished however the mechanism would reset itself ready for the next call, and all trace of the connection would vanish forever. Once exchanges became digital it was a matter of policy and cost whether every single call was logged.

If you wanted to know what calls were originating from a line even a simple recording of that line would include either the DTMF or pulse coding that conveyed the dialed number.

[crypto]

@Mr_Downtown

I don’t believe there would have been any way to know about calls made to a “local” phone number: one in the same exchange or that was not a “toll call.” Law enforcement agencies could get a warrant to install a pen register that would note what numbers someone dialed (something called a trap and trace device did the same thing for noting who called in to the villain’s line).

This would be my guess too. If things were traceable at the local call level, I am sure they would have tracked down the origin of the phine calls made to at least Melvin Belli.

@Mr_Downtown

Calls from central city to suburbs, or between widely scattered parts of a big city, were often toll calls for which a charge was made—and thus a billing record would exist. I don’t know if that was the case for calling Brooklyn from Manhattan, or vice versa.

As a kid, I recall this exact thing. My town was split into two area codes (just a fluke of geography), and if I wanted to call a friend from school about a homework problem, if it was in the wrong area code, there was a seperate charge broken out on the bill. Nothing broken down in our local area.

@Francis_Vaughan

You could trace the origin of a local phone call, whilst it was occurring, by simply getting a technician to walk through the exchange and note down the physical position of the mechanical selectors. The moment the call finished however the mechanism would reset itself ready for the next call, and all trace of the connection would vanish forever. Once exchanges became digital it was a matter of policy and cost whether every single call was logged.

This explains why they couldn’t track Zodiac’s cals. There is no way they could have done this.