After graduating from Bryn Mawr College, she returned to her family home at 108 East 79th Street and attempted to begin a career as a writer.

Arnold's father initially wanted to avoid publicity over his daughter's disappearance, and so sought the help of private investigators in locating her.

After these attempts proved fruitless, the family filed a missing persons report with the New York City Police Department (NYPD) in January 1911.

[8] Arnold's paternal family were descendants of English passengers who arrived in North America on the Mayflower, while her mother hailed from Montreal, Quebec, Canada.

[10][6] Arnold was educated at New York's Veltin School for Girls and attended Bryn Mawr College in Pennsylvania, where she majored in literature and language.

Her friends and family, who were largely amused by her writing aspirations, teased her about the rejection, prompting Arnold to rent a post office box to receive correspondence from magazines and publishing houses.

On the morning of December 12, 1910, Arnold informed her mother Mary that she intended to go shopping for a dress to wear for her younger sister Marjorie's upcoming debutante party.

Arnold charged a half pound box of chocolates to her account at approximately 12:00pm, placed it in her muff and then walked twenty-two blocks (1.4 miles) south to Brentano's bookstore at 27th Street and Fifth Ave.[15] While at Brentano's, Arnold purchased Engaged Girl Sketches, a book of humorous essays by Emily Calvin Blake.

It is speculated that the family was influenced by the 1909 disappearance of Adele Boas, a 13-year-old girl who was reported missing from Central Park and later found to have run away to Boston.

He also found personal letters with foreign postmarks and two folders for transatlantic ocean liners on Arnold's desk, as well as burned papers in her fireplace.

Over the following weeks, Keith visited jails, hospitals and morgues in New York, Boston and Philadelphia, but did not find any sign of Arnold.

As Keith had found literature for transatlantic ocean liners in Arnold's room the day after she disappeared, Pinkerton investigators theorized that she might have eloped with a man to Europe.

[18] After Keith and the Pinkerton investigators could not find Arnold, they persuaded her father to contact the New York City Police Department (NYPD).

"[15] Reporters soon discovered that Francis' comment was in reference to George Griscom Jr., a man Arnold had met while attending Bryn Mawr and with whom she was romantically involved.

In early January 1911, Arnold's mother Mary and her brother John travelled to Italy by ship to forcibly interrogate Griscom.

Upon his return to the United States in February 1911, Griscom told the press that he intended to marry Arnold once she was found and on the condition that her mother approve of the marriage.

[23] That same month, the San Francisco Chronicle reported that clerks at the Anglo-American Hotel had seen a veiled woman they believed to be Arnold.

[24] In the months following the announcement of Arnold's disappearance, Griscom spent thousands of dollars for ads in major newspapers asking her to come home.

[27] Police dismissed his theory because in the days leading up to Arnold's disappearance, the temperature in New York City had dropped to 21 °F and the reservoir had frozen solid.

[29][30] In the days following the announcement of Arnold's disappearance, the NYPD distributed circulars with her picture, physical description and information about the reward throughout the U.S., Canada and Mexico.

In early February 1911, Arnold's father received a postcard signed "Dorothy" bearing a New York City postmark that read, "I am safe."

While the writing matched his daughter's, Francis said he believed that someone had copied her handwriting from samples that were featured in the newspaper and that the postcard was nothing more than a cruel joke.

[32] Around the same time, a jeweler in San Francisco claimed a woman he recognized as Arnold had him engrave a diamond wedding ring for her on January 7, with the inscription "To A.J.A.

The New York World also supported this reasoning after they discovered that Griscom's cousin, Andrew, had jumped to his death from an ocean liner after he had been forbidden to marry an English governess.

This rumor gained some credibility when, in April 1916, an illegal abortion clinic operating out of the basement of a home in Bellevue, Pennsylvania, was raided by police.

Lutz, testified to the New York County District Attorney that Dr. Meredith told him that Arnold had died there after experiencing complications from an abortion.

[22] Over five years after Arnold's disappearance, in April 1916, a convicted felon in Rhode Island named Edward Glennoris (spelled Glenoris in some reports),[36] who was then imprisoned for attempted extortion, claimed that he was paid $250 to bury the body of a young woman in December 1910.

[25] Arnold's father vehemently denied Glennoris' claims, telling reporters, "So far it appears on the face of the man's story, he is talking utter nonsense.

"[13][40] According to Keith, Dorothy's mother Mary did not share her husband's opinion that their daughter had been murdered and remained hopeful that she was still alive.

[43] In her young adult novel Lost (2009), author Jacqueline Davies combines the story of Arnold's disappearance with that of the Triangle Shirtwaist Factory fire.