In the name of the law, cash me! My life with Mexican Cops

Going to the authorities in Mexico to report that you were mugged and robbed by a policeman is like complaining in the Vatican that you were molested by a priest. But my Mexican friend insisted that this had to be sorted out. Otherwise, his other solution was to get armed and go to where the tracking said my cell phone was at the moment - a neighborhood that has a reputation too bad even for Mexico. So I agreed to go to the prosecutor's office.

"You probably don't remember what he looked like, do you?"
"Well... kind of short, fat, round-headed," I flipped through my memory after last night. True, it was a little leaky due to all the mezcal. But mainly, though, I spent most of the fateful moment pinned against the wall, where I couldn't get much of a look at the son of a bitch. I didn't even have a reason to at that point, I believed until the last moment that it was a normal "inspection", which I had experienced many times in Mexico, therefore he would just take the few hundreds I had in my wallet and I would go home in peace and at worst swear.
"Hm... Well, that won't help us much, that's what every cop looks like here," was the reply.

It was the first time I'd ever filed a criminal complaint against a cop. I wasn't even planning on going through with it, it was going to get swept under the rug anyway. So I didn't expect anything from it - least of all that someone would go to the snake's nest where my three-month-old cell phone was supposed to be resting in peace.

But we did have one ace up our sleeve: The bastards, sorry cops, had ambushed me on one of the busiest nighttime streets in central Ciudad de México, riddled with security cameras. So, if anyone wants to, they can just go through the footage from that time and no doubt find out at least which patrol was patrolling the street at that moment. Let's assume the bastards were smart enough to pick a place where the cameras couldn't see them robbing drunken party-goers at night.