SANTA FE, N.M.—Investigators plan to discuss their initial findings Wednesday in the fatal movie-set shooting in which Alec Baldwin fired a prop gun, killing a cinematographer and wounding the director. The news conference by Santa Fe County Sheriff Adan Mendoza and District Attorney Mary Carmack-Altwies promises the first detailed public comments by investigators about the killing of 42-year-old Halyna Hutchins during a rehearsal at a New Mexico ranch. Court records say that an assistant director, Dave Halls, grabbed the gun from a cart and handed it to Baldwin, indicating the weapon was safe by yelling “cold gun.” But it was loaded with live rounds, according to a written affidavit from a detective. Baldwin, 63, who is known for his roles in “30 Rock,” “The Departed” and “The Hunt for Red October” along with the impression of former President Donald Trump on “Saturday Night Live,” has described the killing as a …