Hi:
The FBI designed and used this style holster for dress suits which was the type dress up until J. Edgar Hoover was no longer in charge.
The "Draw" was with the knees slighty bend and taking a step to the left.
This movement allowed the suit coat to swing open and the "Draw" was made. With the knees still slighty bent, the drawn revolver was brought to the center of the shooter's body, pointed, and fired.
This holster cant was used for uniform use, however was fairly easy for a suspect to gain control of the weapon when the suspect was being subdued.
The FBI holster did not use a holster retaining strap but the holster for uniforms did. I used a "Jordan" border patrol style for years using a revolver
but others favored the FBI type or a cross draw.
Jimmy