There's a Sicilian Mafia killing method where they would tie someone up making them strangle themselves. Anyone knows exactly how it works?

I believe you're talking about the brutal murder of Irving "Puggy" Feinstein by Abe Reles for Murder Incorporated in 1939. I've attached the best description I could find, I want to say I've seen an illustration or photo image of how it was done but I couldn't find it yet.

It is a time-honored underworld method of killing. Actually, its a particularly vicious way to kill someone because they actually kill themselves through self-strangulation.

They are "trussed up" by wrapping their two legs together and roping their ankles together, running the rope tightly up through their back and then looping a sliding hangman's type knot around their neck. Their hands are tightly bound behind their back of course so they cannot move or free themselves.

The rope is then pulled extremely tight behind them from their head to their wrapped feet, forcing their head and neck backwards, and their feet and legs to be bent backwards as well.

A person cannot hold themselves in that awkward position for even a few minutes. As they lose their strength in their legs and both their neck and legs naturally pull forward extending, the victim strangles himself with the taut rope that is pulled higher and tighter by the mans own body weight. They also struggle to get free which only serves to tighten that death rope faster.

Its a form or torturing a guy who you wanna fuck with. Or what we call in New York giving a guy his "buckwheats."

Okay, I know the method was often used in Sicily but I suppose it's universal.

Here's some more info.
"Incaprettamento is a ritual strangulation that represents a method of homicide typical of the Italian Mafia. While the victim is in the prone position, he/she is bound by one end of a rope, creating a slipknot around the throat, while the other end is used to tie the limbs behind the back. Forensic investigations reveal that in most cases, the binding of the extremities and the positioning of the victim are carried out after death due to others means and are intended to hold somebody in contempt and to punish betrayers. When the victim is tied while alive, the death is caused by self-strangulation because it is impossible to maintain the legs in this forced position. Here, we describe in detail a case with a lot of similarities to incaprettamento, although we define it as atypical because of the unusual methods of the actual binding and the circumstances in which death occurred. In fact, the investigation of the crime scene, the external and internal findings, and the histologic examination result show that this is a crime of passion."
https://pubmed.ncbi.nlm.nih.gov/24457582/

This was the execution method shown in a pretty decent Mafia movie, "The Brotherhood," by a Sicilian Don (played by Kirk Douglas) as vengeance against a Napolitan' (played by Luther Adler) for an ancient massacre:


https://www.youtube.com/watch?v=UfnScwoB4SY

Reles was a real thug--"the canary who could sing but couldn't fly."

Also depicted in the 1995 movie "Sugartime",loosely based on the relationship between Sam Giancana and Phyllis McGuire.

There are many instances through history of guys who were whacked out in this manner. Another term used to connote this is being "hog-tied"

Many times when you find a guy dead a car trunk he was also half trussed up in this way. They just don't report it as such.

Brutal. What a fucked up way to die