Marie, then 30, told the detectives that both children got along well with Feilong and that C.T. even called him "Daddy."
Questioned separately, Feilong, then 26, said the only arguments he had had with Marie were about her smoking. He wanted her to quit.
The detectives learned that Feilong, a former member of the Chinese national diving team, had come to this country under the sponsorship of the National Collegiate Athletic Assn. He and Marie met in 1994 as college students in Austin, where he was an assistant diving coach at the University of Texas. They were married the following year.
They moved to Southern California in 1996 after he was offered a job with the Mission Viejo Nadadores, an amateur water sports club that has produced a dozen Olympic gold medalists. The family had been living in the Villa Marguerite apartments for three weeks when C.T. disappeared.
By focusing on the Wus initially, detectives were going by the book. Crime statistics show that when small children die violent deaths, family members or caregivers are most often responsible.
Looking into Feilong's employment, investigators found what they considered further cause for suspicion. Because he was in this country on a student visa and lacked a work permit, the aquatic club had put Marie on its payroll and was issuing paychecks in her name.
Det. Tom Giffin confronted her about this the morning after C.T.'s disappearance. While searchers continued looking for the boy, investigators had brought the Wus to a sheriff's station in Laguna Niguel for further questioning.
Giffin told Marie that by collecting a paycheck from the Nadadores, she was committing fraud. He suggested that if the couple practiced deception on such mundane things, they might lie about serious things too.
"Do you all really suspect Feilong?" Marie asked.
"He's not above suspicion," Giffin replied, according to a transcript of the 72-minute session. "What we'd like to do is have you interviewed on a polygraph."
"Oh, I'd love it," Marie replied. "Right now."
Feilong, who was interviewed in a separate room for 45 minutes, also agreed to a polygraph, but not before questioning whether the results would be reliable.
"You know, we had a long day yesterday, and we didn't sleep last night," he told Giffin. "We're emotional and we are upset."
That afternoon, Feilong and Marie were brought to Brea police headquarters, where a sergeant, Tom Flenniken, conducted polygraph tests for the Sheriff's Department.
As Feilong had expected, his exam did not go well. Flenniken reported that Feilong showed signs of deception when he denied harming C.T. or knowing the child's whereabouts.
Standards adopted by the two national associations of polygraph operators say that suspects should not be tested the same day they are interrogated.
Dan Sosnowski, spokesman for the American Polygraph Assn., said a delay of several days or a week is advisable. "Doing it the same day is an absolutely terrible way to conduct a good exam," he said. "The person is just too emotionally wound up."
Linda J. Quinonez, a board member and former president of the American Assn. of Police Polygraphists, said: "The tests should never have been administered on the same day they had been interrogated."
Flenniken, who has not been certified by either organization, declined to comment.
Marie's polygraph showed no signs of deception. It was now after 10 p.m. Sheriff's Det. Mark Simon told Marie that C.T.'s body had been found seven hours earlier in dense brush near the east bank of Oso Creek, a quarter-mile northeast of the Wus' apartment.
"Oh my God," she said.
"OK, I do want to tell you, Marie, that I suspect your husband," Simon said.
"I don't," she replied. "He didn't do it."
The Body's Signs
The detectives' hunch was that Feilong had smothered C.T. sometime after Marie went to sleep on Sunday, Aug. 11, 1996, and that he had carried the child's body to its resting place beside the creek.
In questioning the couple, detectives probed various theories as to what might have triggered the killing. Perhaps Feilong was angry because he thought Marie was spoiling the boy. Perhaps C.T. had interrupted the couple's lovemaking that night.
Results of an autopsy conducted Wednesday, Aug. 14, the day after the body was discovered, fortified investigators' suspicions. C.T.'s stomach contained lumps of what appeared to be hot dog meat. The Wus had said they fed him hot dogs between 7:30 and 8:30 p.m. Sunday.
To autopsy surgeon Richard I. Fukumoto, the limited degree of digestion indicated that the child had died two to four hours after eating. That would place the time of death no later than 12:30 a.m. Monday, which meant that C.T. could not have been alive at 7:30 that morning, as Feilong maintained.
But Fukumoto's findings did not mesh with those of deputy Orange County Coroner Richard McAnally, who examined the boy's body shortly after it was found in the ravine.