Editor's note: This is the first in a four-part series on infamous Bay Area murders of yore. A new story will be published each Friday in October.

James P. Watson was new in town and in the market for another wife.

His favorite method of procuring a spouse was through the classifieds. It was a common practice in 1919, with a whole section of the newspaper dedicated to “matrimonials.”

So it’s likely that Watson placed an ad or two in the San Francisco periodicals.

"Would be pleased to correspond with refined young lady or widow,” read one he’d used in Washington the year before. “Object, matrimony. This advertisement is in good faith."

Nina Lee Deloney, a 43-year-old widow a few years younger than Watson, responded. The courtship, as it always did with him, moved swiftly. He would have taken her for rides in his fancy car. Showered her with flowers and candy and perfume. Made promises of a lavish Hawaiian honeymoon.

In December 1919, they were married in Oakland. It must have felt like a bright, new chapter for Nina. Watson was wealthy, doting and interesting, and a federal secret service agent, he told her.

Even after it was all discovered — the dozens of marriages, the brutal murders — his surviving wives still spoke breathlessly about him.

The man, they said, was a real romantic.

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James P. Watson was born Charles Gillam in 1871. As he told it, his childhood was characterized by mental and physical abuse. His father was absent, and his mother was volatile. After she remarried, she changed young Charles’ name — first and last. He became Joseph Holden. But this new name did not blend him into his new family. His step-father tormented him and the boy left home at age 12.

He drifted for the next two decades, eventually reemerging in Canada with another identity: James Watson. In 1913, he took his first wife: Katherine Kruse of British Columbia. One day, he disappeared. She was lucky.

In 1918, he took at least three wives, two in Canada and one in Seattle. Marie Austin of Calgary was the first to die. On a vacation in Coeur d'Alene, he bludgeoned her to death then weighted her body with rocks, sinking her to the bottom of a lake. The Seattle wife was next to go — and fast. For their honeymoon, they took a trip to see a waterfall near Spokane. As she admired the view, her husband came up behind and gave her a firm push.

"There was no controversy,” Watson later told detectives. “Just an impulse."

In 1919, he added more wives: Maude Goldsmith in January, Beatrice Andrewartha in February, a Sacramento woman (he’d forgotten her name), a lady from Vancouver (her too), Elizabeth Prior in March, Bertha Goodrich in June, and Alice Ludvigson in July.

Beatrice he drowned in Lake Washington. Elizabeth he beat to death with a hammer. Bertha and Alice were held underwater under they died.

"We were by the lake and an impulse came over me,” he said of Bertha. “I hit the girl. Something said: 'Go ahead,' and I went ahead. It was just getting dusk."

When police asked Watson how he’d kept so many women simultaneously, he told them matter-of-factly that he pretended to be a government agent. “Work” took him away frequently. He’d use his work trips to see his other wives, sometimes up to four in the same town. Money was no problem: One of the first things Watson always did was make sure his new wife signed over her assets and changed her will.

No one, not even Watson, knows how many women he married. He guessed it was about 19 in three years. Some have estimated it was closer to 40. But one thing he knew: The Pacific Northwest was getting too crowded with Mrs. James Watsons.

In 1919, he left for California where he married Nina and at least two other women. He kept moving south, taking Nina with him. One day, she discovered a letter from another paramour. Watson crushed her skull in with an ax, burying her body in the desolate Imperial Valley.

His next wife took a different tack when she became suspicious: She hired a private investigator. The Nick Harris Detective Agency of Los Angeles thought her case was more of the usual marital drama. She said she was afraid of her husband, a federal agent, partially because he kept a black satchel she couldn’t open.

The PIs waited for one of his “business trips” before sneaking into the home. When they cracked the bag open, they found a trove. Jewelry, marriage licenses, half a dozen wills — some signed and some blank — and correspondence with 20 more women he planned on meeting and marrying.

When Watson returned, he was arrested by Los Angeles police. They charged him with bigamy.

Then, he started confessing.

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Decades before the term “serial killer” was coined, Watson defied all conventional medical and psychological understanding. Dozens of interviews and doctor’s visits failed to unravel his psyche. Some experts thought he was out of his mind; others found him disturbingly sane. He was unlike anything they’d ever seen.

Calmly, he told police about the homicidal trail he’d created up and down the West Coast. At first, they thought he was bluffing. It wasn’t until he led them to Nina’s body that they began to believe. Investigators in Washington and Canada confirmed women had gone missing, never to be found. Watson proudly told police if you weighed down bodies in very cold water, they wouldn’t rise to the surface. He was right. The bodies were never found.

When asked why he would keep so much incriminating evidence, he shrugged his shoulders. “I cannot explain why,” he said.

Thanks to modern studies of multiple murderers, we do know why: They were trophies, reminders of the crime that let killers concretize and relive the moment. His motives then were a mystery, but today match the pattern of many documented killers. There was a straightforward practical component — monetary gain — and a sexual one — the thrill of tricking, then killing, unsuspecting women.

As to why he confessed when he’d only been charged with bigamy, he likely reached what is known as the “burn out” stage.

“Serial killers sometimes do burn out,” writes Peter Vronsky in “Serial Killers: The Method and Madness of Monsters, “and depending on the personality of the individual they either allow themselves to be captured, commit suicide, or cease killing on their own.”

Watson took a plea deal. In 1920, he was sentenced to life in prison.

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“Adonis' charms found lacking in Bluebeard,” the San Francisco Chronicle trumpeted when he arrived at San Quentin.

Watson was not the Lothario the public imagined. He stood 5-foot-9, a shade over 120 pounds. He was so thin his chest caved inward. A 1922 "Journal of Criminal Law and Criminology" study of Watson described him as mild-mannered. The other inmates and prison guards couldn’t comprehend how he’d beguiled so many well-educated, cultured women.

“I had to turn away a number of women who had no legitimate reason for calling, but faked excuses in the hope of getting a chance to see him,” San Quentin warden James A. Johnston bemoaned to Esquire in 1946.

While imprisoned, Watson took up writing. He repeatedly tried submitting poems to the New York Times. One, ominously, was called “My Ideal Wife.”

In 1939, he wound up in the San Quentin infirmary with pneumonia. He died shortly thereafter. His will stated that his $80,000 in cash, bonds and valuables would be distributed among current and previous prison wardens, the Salvation Army and a few random others. He claimed the location of this fortune was encoded in another letter. No clues were ever found.

The warden assumed it was Watson’s final lie. All he left behind was $18.70 in his prison bank account and one last, strange sentence in the will about his marital status.

“I am,” Watson wrote, “a widow.”

Katie Dowd is an SFGATE Senior Digital Manager. Email: katie.dowd@sfgate.com | Twitter: @katiedowd