On Oct. 23, Mark David Chapman, a pudgy young man who likes cartooning, travel and rock music, signed out for the last time as a security guard at the apartment building at 444 Nahua St. in Waikiki's tropical garden of skyscrapers.

On the sign-out sheet Chapman scrawled the name "John Lennon." No one thought much of it at the time, little jokes being little jokes.

Four days later, Mark David Chapman, who collects Dali prints and who used to show slides of his worldwide travels to his coworkers at lunchtime, drove to a downtown Honolulu gun shop and purchased a .38-caliber "Undercover" handgun similar to the stubbarreled Smith & Wesson favored by police detectives.

No one thought much of that, security guards being security guards. The police issued the permit rapidly and smoothly.

Some time after that, Chapman left on another of his trips. But no one thought much of that -- not even his wife, Gloria, who was a travel agent when she met him in Honolulu and started their romance by selling him airline tickets.

By last Sunday, Chapman was in New York, with a borrowed $2,000 and the stub-nosed handgun in his pocket. He checked into a $75-a-night room in the Sheraton Centre where yesterday, two days later, no one could remember who he was.

But by yesterday everyone was straining for memories of Mark David Chapman, another obscure young American with a gun, another strange young man for whom the pieces didn't fit.

"Mr. Lennon?" Chapman inquired late Monday night of the man whose music he had been drawn to, along with Jesus, during his high school days in Georgia.

Lennon, near the iron gate at the entrance to his luxury Manhattan apartment building, turned toward the young man. Chapman held the .38 in both hands, dropped into the combat crouch of a Hawaii Five-O detective and fired several times, ending the life of the musican he had loved during his teens in Decatur, Ga., and putting a finis to the Beatles record collection he amassed as a boy.

Childhood friends in Georgia remembered Chapman yesterday as a youngster who went through a "hood" stage in the 9th or 10th grade. "You know, long hair, old Army jackets, that kind of thing," recalled a former classmate, Walter Hendrix, now the minister of music at a Baptist church in Smyrna. "But then he changed," Hendrix said, becoming a bit of a "Jesus freak."

Another former classmate, Robert Wayne, said Chapman was "very quiet and very kind. He was not a freak. He became very religious in his junior and senior year. Eight years can do a lot to a person. People change, but he was a nice person when he was in high school."

Manhattan Assistant District Attorney Kim Hogrefe said yesterday that Chapman came to new york to perform a "deliberate premeditated execution" and acted in a "cool, calm and calculated" manner.

New York authorities said Chapman had twice tried to commit suicide. Criminal Court Judge Martin H. Lettinger committed him to Bellevue Hospital for a 30-day psychological evaluation, saying he should be placed on a "suicide watch."

Chapman's former boss at the Castle Memorial Hospital in Kailua, on the windward side of Oahu, described the 25-year-old suspect as "very creative," a young man who played the guitar and was well-liked by his coworkers, to whom he showed slides of his travels to the Orient and London.

Friends and former bosses in Georgian and Hawaii said they didn't believe that the Mark David Chapman they knew could have shot Lennon.

Chapman's court-appointed attorney, Herbert Adlerberg, said his client "did shoot him. Yes. I would characterize the man as a very confused individual. He doesn't understand himself."

Police in Honolulu said there was nothing unusual about issuing a gun permit for Chapman. Gun permits are issued routinely to persons with no criminal record, they said.

Yesterday in Honolulu, where Chapman lived in a $450-a-month high rise, Gloria Abe Chapman said she had heard about the shooting of Lennon but didn't know where her husband was. Then she went into seclusion. A friend said Mrs. Chapman would say no more because her "health was in danger."

Yesterday in Atlanta, Chapman's father, David Curtis Chapman, a bank employe, went into seclusion.

None of his friends or relatives appeared to know where Chapman had been.

Yesterday in New York, Mark David Chapman stood mute before the judge. He walked into court with a waddling gait. He wore a V-neck sweater, wire-rim aviator glasses and a blank look.

"This defendant is not fully cognizant of what is happening to him at this time," his attorney said.

Hogrefe, the assistant district attorney, said Chapman had arrived in New York after he "borrowed a substantial sum of money -- $2,000 was found on him at the time of his arrest -- for the purpose of coming to New York City to do what he has done."

What he had done was stop the music, the way a predecessor had ended Cemelot, the way a prototype had stopped Martin Luther King Jr.'s dream, the way dreams were ending in too many places lately.