Black Dahlia 2

An autopsy of Short's body was performed on January 16, 1947, by Frederick Newbarr, the Los Angeles County coroner. Newbarr's autopsy report stated that Short was 5 feet 5 inches (1.65 m) tall, weighed 115 pounds (52 kg), and had light blue eyes, brown hair, and badly decayed teeth. There were ligature marks on her ankles, wrists, and neck, and an "irregular laceration with superficial tissue loss" on her right breast. Newbarr also noted superficial lacerations on the right forearm, left upper arm, and the lower left side of the chest.

The body had been cut completely in half by a technique taught in the 1930s called a hemicorporectomy. The lower half of her body had been removed by transecting the lumbar spine between the second and third lumbar vertebrae, thus severing the intestine at the duodenum. Newbarr's report noted "very little" ecchymosis (bruising) along the incision line, suggesting it had been performed after death. Another "gaping laceration" measuring 4+1⁄4 inches (110 mm) in length ran longitudinally from the umbilicus to the suprapubic region. The lacerations on each side of the face, which extended from the corners of the lips, were measured at three inches (75 mm) on the right side of the face, and 2+1⁄2 inches (65 mm) on the left. The skull was not fractured, but there was bruising noted on the front and right side of her scalp, with a small amount of bleeding in the subarachnoid space on the right side, consistent with blows to the head. The cause of death was determined to be hemorrhaging from the lacerations to her face and the shock from blows to the head and face. Newbarr noted that Short's anal canal was dilated at 1+3⁄4 inches (45 mm), suggesting that she might have been raped. Samples were taken from her body testing for the presence of sperm, but the results came back negative.

On January 21, 1947, a person claiming to be Short's killer placed a phone call to the office of James Richardson, the editor of the Examiner, congratulating Richardson on the newspaper's coverage of the case and stating he planned on eventually turning himself in, but not before allowing police to pursue him further. Additionally, the caller told Richardson to "expect some souvenirs of Beth Short in the mail".

On January 24, a suspicious manila envelope was discovered by a U.S. Postal Service worker. The envelope had been addressed to "The Los Angeles Examiner and other Los Angeles papers", with individual words that had been cut-and-pasted from newspaper clippings; additionally, a large message on the face of the envelope read: "Here is Dahlia's belongings, letter to follow". The envelope contained Short's birth certificate, business cards, photographs, names written on pieces of paper, and an address book with the name Mark Hansen embossed on the cover. The packet had been carefully cleaned with gasoline, similarly to Short's body, which led police to suspect the packet had been sent directly by her killer. Despite efforts to clean the packet, several partial fingerprints were lifted from the envelope and sent to the FBI for testing; however, the prints were compromised in transit and thus could not be properly analyzed. The same day the packet was received by the Examiner, a handbag and a black suede shoe were reported to have been seen on top of a garbage can in an alley a short distance from Norton Avenue, two miles (three kilometers) from the crime scene. The items were recovered by police, but they had also been wiped clean with gasoline, destroying any fingerprints.

On March 14, an apparent suicide note scrawled in pencil on a bit of paper was found tucked in a shoe in a pile of men's clothing by the ocean's edge at the foot of Breeze Avenue in Venice. The note read: "To whom it may concern: I have waited for the police to capture me for the Black Dahlia killing, but have not. I am too much of a coward to turn myself in, so this is the best way out for me. I couldn't help myself for that, or this. Sorry, Mary." The pile of clothing was first seen by a beach caretaker, who reported the discovery to lifeguard captain John Dillon. Dillon immediately notified Captain L. E. Christensen of West Los Angeles police station. The clothes included a coat and trousers of blue herringbone tweed, a brown and white T-shirt, white jockey shorts, tan socks and tan moccasin leisure shoes, size about eight. The clothes gave no clue about the identity of their owner.

Police quickly deemed Mark Hansen, the owner of the address book found in the packet, a suspect. Hansen was a wealthy local nightclub and theater owner and an acquaintance at whose home Short had stayed with friends. According to some sources, Hansen also confirmed that the purse and shoe discovered in the alley were in fact Short's. Ann Toth, Short's friend and roommate, told investigators that Short had recently rejected sexual advances from Hansen, and suggested it as potential motive for him to kill her; however, he was cleared of suspicion in the case. In addition to Hansen, the Los Angeles Police Department (LAPD) interviewed over 150 men in the ensuing weeks whom they believed to be potential suspects. Manley, who had been one of the last people to see Short alive, was also investigated, but was cleared of suspicion after passing numerous polygraph examinations. Police also interviewed several persons found listed in Hansen's address book, including Martin Lewis, who had been an acquaintance of Short's. Lewis was able to provide an alibi for the date of Short's murder, as he was in Portland, Oregon, visiting his dying father-in-law.

A total of 750 investigators from the LAPD and other departments worked on the case during its initial stages, including 400 sheriff's deputies and 250 California State Patrol officers. Various locations were searched for potential evidence, including storm drains throughout Los Angeles, abandoned structures and various sites along the Los Angeles River, but the searches yielded no further evidence.[68] City councilman Lloyd G. Davis posted a $10,000 (equivalent to $131,058 in 2022) reward for information leading police to Short's killer. After the announcement of the reward, various persons came forward with confessions, most of which police dismissed as false. Several of the false confessors were charged with obstruction of justice.

By the spring of 1947, Short's murder had become a cold case with few new leads. Sergeant Finis Brown, one of the lead detectives on the case, blamed the press for compromising the investigation through journalists' probing of details and unverified reporting. In September 1949, a grand jury convened to discuss inadequacies in the LAPD's homicide unit based on their failure to solve numerous murders—especially those of women and children—in the previous several years, Short's being one of them. In the aftermath of the grand jury, further investigation was done on Short's past, with detectives tracing her movements between Massachusetts, California and Florida, and also interviewed people who knew her in Texas and New Orleans. However, the interviews yielded no useful information in the murder.