It began with a story in a New York paper two years ago—Veronica Brunson, just 12 years old, had been found dead in the Times Square area. She was a prostitute and had "apparently fallen" from a hotel window. The account "intrigued" Sandy Johnson, a former actress and mother of three sons, "in a horrible kind of way," she remembers.

Johnson got in touch with the investigating detectives and soon became convinced that Veronica had been pushed to her death. The police referred to the case as a CUPPI, for Circumstances Undetermined Pending Police Investigation—it could not be classified as either homicide or suicide. Last year there were 242 CUPPIs in New York. The commanding officer of the third homicide zone, Lt. Richard Gallagher, challenged Johnson to prove her suspicions. "Be my guest," he said. "You bring me the collar [the evidence to justify an arrest] and we'll upgrade it to a homicide." Although Johnson ultimately failed in her mission, she came away with a stirring fictionalized version of the case, The CUPPI (Delacorte, $8.95).

Teaming up with an undercover policewoman, Johnson even masqueraded as a streetwalker during her research. She was hoping to be approached by a pimp who might have information about Veronica. "The first night nothing happened," she says. "The next night I wore more makeup and stuffed my bra. By the fifth night still nothing. I asked my partner what I was doing wrong. She told me to look behind me. All I saw was a bunch of taxicabs. All of them turned out to be driven by cops. She said, 'Half the damn department is out here watching you. They don't need a writer blown away. You think the pimps don't know who they are?' " (Meanwhile the attractive Sandy had no trouble attracting Johns, who always fled at the glimpse of a police badge.)

Finally she did learn the identity of Veronica's pimp from a prostitute. The woman told how he had bragged about throwing the child out the window because she wouldn't follow his orders. "That wasn't enough evidence," Johnson admits. "I kept hoping the book could end with him hanging by his toenails—it hasn't happened. But I did get to know the girls. They're eager to talk. Their stories followed a sort of pattern. They have been beaten, sexually molested or, at the very least, ignored. When they hit the street the pimps are there to listen. In 15 minutes a pimp can give a girl everything she didn't get in 15 years at home."

By comparison, Johnson's childhood was elegant. The daughter of a Philadelphia investor, she recalls "only three rules in the house—don't chew gum, don't put your hands in your pockets and don't whistle." After a brief first marriage while attending the University of Pennsylvania, she became an actress, appearing on Ironside, Mannix and the soap Search for Tomorrow. "Acting never did much for my ego," the fortyish Johnson says. "When I realized I could write and do it in pajamas, this was for me." Her first efforts were TV scripts.

Johnson, who is divorcing her present husband, lives in an apartment on Manhattan's East Side. Sons Mark, 20, Billy, 18, and Anthony, 13, are away at school. Her current man is Jack O'Connor, head of a security company (a current client is the hospitalized Shah of Iran). O'Connor sought out Johnson after reading her book and is using his firm to continue the investigation into Veronica's death (which is still officially listed as a CUPPI).

"We are not doing this because the police haven't done their job," Sandy explains. "But CUPPIs are given routine investigations. There just aren't enough police to devote to unexplainable deaths. We know the man responsible for this murder. We know where he is. We have his photograph. I want him to pay."