NEW YORK, DEC. 23 -- After deliberating for more than 100 hours, the jury in the seven-week Howard Beach murder trial found the last pieces of the puzzle in the testimony of three seemingly peripheral witnesses.

The recollections of Alex Rios, an inarticulate night watchman at a nearby bank; Valerie Sampson, a 911 emergency operator, and Scott Fried, a passer-by, were crucial to the jury's effort to reconstruct the sequence of events in which four white teen-agers were accused of chasing a black man to his death on the Belt Parkway.

The jury returned its verdict Monday night, finding three of the teen-agers guilty of manslaughter in the death of Michael Griffith.

"The main thing is Michael Griffith's death, in our opinion, was caused by the fear generated from the chase," juror Chester Li said in an interview in his home in Bayside, Queens. "It was that chasing which caused his death.

"Some people were very confused about this," said Li, 62, a Chinese immigrant who works as an insurance actuary. "Some people said, 'Is it possible that this death was caused solely by the reckless driving of the motorist?' We strongly believed that no motorist would be able to avoid a man who jumped out from the divider."

The marathon deliberations by the seven men and five women produced manslaughter convictions for Jon Lester, 18, Scott Kern, 18, and Jason Ladone, 17, while acquitting Lester and Kern of murder. The three were also found guilty of assault in the baseball-bat beating of Griffith's companion, Cedric Sandiford. Defendant Michael Pirone, 18, was cleared of all charges.

Li said the jury spent the first several days sorting out confusing and conflicting testimony from about 80 witnesses. "There were so many inaccuracies on both sides that it's the jury's duty to find out which were lies," Li said.

Lawyers on both sides emphasized during the three-month trial that the murder and manslaughter charges hinged on the credibility of Robert Riley, 18, who testified against his former friends. But Li said the jury paid scant attention to his long testimony.

"We were instructed not to use his testimony as the sole basis of judgment because he is a so-called accomplice," Li explained.

Instead, he said, the jurors concentrated on mapping the chase scene in their minds, with the aid of enlarged maps and diagrams of the Howard Beach section of Queens. "Some of us were not clear on the route of escape of the victim," Li said.

Defense attorneys cited Sandiford's original account, given to police after he was beaten, that Griffith did not flee to the parkway along the street where witnesses saw the youths running. Sandiford changed his account at the trial, saying that he had been confused, but the defense continued to insist that Griffith took a circuitous route to the parkway and was several blocks from the teen-agers when he died.

Enter the bank guard, the 911 operator and the passer-by. Courtroom observers were mystified when the jury asked, on Days 5, 6 and 8 of its deliberations, to rehear their testimony, but Li said this week that they provided the key details on when the chase began at a neighborhood pizzeria and when Griffith was hit on the highway.

After several more days of discussion, Li said, the jury agreed that in the time elapsed, Griffith could not have run farther than the route outlined by the prosecution.

Jurors disagreed on several issues throughout the 12 days of deliberations, Li said. In the beating of Sandiford, he recalled some jurors asking, "If only one held a baseball bat, how can all three defendants be guilty of assault in the first degree?"

To resolve that point, the jury several times asked the judge to repeat his legal instructions on the assault charge, baffling courtroom observers. "The three faced the blacks together, as a group," Li said. "The charge said you are guilty if you're 'acting in concert,' it doesn't matter who held the bat. We asked for the charge several times in order to hear that phrase."

The jurors acquitted two of the defendants of second-degree murder, and three of attempted murder in the beating of Sandiford, because they felt that the teen-agers were out to teach the blacks "a lesson" and did not intend to kill them, Li said.

The jury knew that its lesser manslaughter and assault verdicts would not play well in either black or white communities, Li said, and some of the female jurors cried after hearing the sobs and shrieks of the defendants' families.

When a black spectator shouted "murderers, murderers" and security guards dragged him from the courtroom, the jurors feared for their safety, Li said.

Most members of the jury, which included six whites, two Hispanics, two Asians, one East Indian and one black, have remained in seclusion or have left town to avoid further publicity.

Despite the mixed reviews the verdicts have drawn, Li said the jurors stand by their judgment. "I think this verdict is good for the country as a whole; for whites, for blacks, for Chinese, for everyone," he said.