"El Diablo" is actually Spanish for "The Devil". "The Prince of Darkness" in Spanish is "el príncipe de la oscuridad".
Javier Gitan is charged with two counts of murder in the second degree for being hired to kill a former cartel member, and his wife. Murder for hire, and killing more than one person in the same criminal act, both constitute murder in the first degree.
Both the NYPD ballistics expert, and Sergeant Ceretta, consider it unusual that someone was shot and killed with a .38. However at the time this episode aired the .38 Special was the most popular handgun cartridge in the world, this is the caliber of handgun that nearly all law enforcement carried at the time, and was also a very popular civilian gun, both among law abiding gun owners and criminals; along with .22's a .38 snub nose was the most commonly used "drop piece" by gangs and drug dealers. If a dead body with a GSW is found odds are they were shot by either a .22, .380, .38 or 9mm. By the turn of the 21st century the .38/.357 had been supplanted by the 9x19mm Parabellum as the most common handgun caliber after law enforcement, and many civilians, changed to semi-automatics; but it is still the most common bullet caliber used in revolvers, as both the .38 Special and .357 Magnum use that same bullet.
The gun "Elvis" uses is a Steyr AUG (pronounced "Steye-er A-U-G"). Everyone keeps mispronouncing it as "st-air aweg".