After 11 days of intensive investigation, D.C. Police yesterday were still piecing together evidence in the puzzling death of a five-month-old girl who apparently drowned in a bathtub at the Capital Hilton Hotel on April 16.

Homicide detectives, prosecutors and others involved in the case continued to be tight lipped about details, but these new developments were learned.

Investigators say they have largely discounted the claim of the child's mother, Berit Melin, a 29-year-old Swedish citizen visiting the United States, that a knife-wielding intruder forced his way into her hotel room and drowned the baby when she failed to respond to his demands for a large sum of money.

Melin was admitted to Washington Hospital Center early this week for psychiatric observation. Officials would not say why this decision was made, but several police sources said the woman appeared confused, hampering the investigation.

Melin's passport and that of the child's father, Stockholm gem dealer Lars Levin, described by police as Melin's fiance, are being held by police, restricting their movement.

Several witnesses including Levin, homicide detectives and technicians from the D.C. Police mobile crime laboratory, were called to testify this week before a Superior Court grand jury. Officials stressed that the grand jury action does not mean they are seeking an indictment.Use of the grand jury, they said, simply provided a formal setting for the taking of sworn testimony, unlike a police station interrogation room.

One source said both Melin's admission to Washington Hospital Center and the surrender of Levin's and Melin's passports were voluntary "to the extent they were not pursuant to a court order."

While the investigation has proceeded quietly, it has drawn high-level attention. Deputy Police Chief William Trussell, commander of detectives for the police department, has personally directed much of the investigation.

Executive Asst. U.S. Attorney Henry Schuelke, third-ranking official in the prosecutor's office here, is working closely with police.

Richard A. Hibey, a private attorney whose law firm has represented the Swedish Embassy here, is now representing both Levin and Melin. Hibey said the embassy asked his firm "to give the couple an opportunity to consult with counsel."

Swedish embassy spokesman Las Arno said Levin, Melin and their five-month old daughter, Lilly-Sophie, came to the United States from Stockholm about three weeks ago for a "mixture of vacation and business."

They stopped in New York first where Levin apparently conducted business in connection with his gem dealing. The three then came to Washington on Friday, April 13, checking into the Capital Hilton at 16th and K Streets NW. Police said Levin had a quantity of gems which he placed in the hotel safe.

Melin told police that an intruder armed with a knife forced his way into the fourth-floor hotel room at about 12:30 p.m. on Monday, April 16, while Levin was away from the hotel. She said he demanded a large sum of money.

She offered the small amount of American and Swedish currency in her purse, but the intruder continued to demand a larger amount, Melin told police. To enforce his demand, he took Melin's baby from the crib, turned water on in the bathtub and threatened to drown the child, Melin told police.

After repeated threats during which Melin said she had no more money, the intruder, "placed the baby in the tub" and then fled, according to a police description of Melin's account.

With the child still apparently in the tub, Melin left the room to seek help, police said. She returned with hotel security personnel who discovered the baby in the tub and called an ambulance. The baby was pronounced dead on arrival at Children's Hospital National Medical Center.

Police said the baby had been found nude and floating face down in the tub. The tub water was about six inches deep, they said.

An autopsy on the child showed evidence "consistent with what we usually find in other drowning cases," said D.C. Medical Examiner James Luke, but he added that further tests are being conducted.

Levin, according to police, had been visiting the national headquarters of B'nai B'rith, the Jewish social service organization at 1640 Rhode Island Ave. NW, when the hotel incident occurred.

Daniel Thursz, executive vice president of B'nai Brith, said a security guard log book at the building's entrance shows Levin signed into the building at noon and signed out 58 minutes later. Thursz said Levin apparently visited the building's museum and perhaps some general offices, but had no appointments to see specific B'nai B'rith officials.

Levin could not be reached for comment about the case. Hibey, the attorney for Levin and Melin, said he could not comment while the matter is under investigation.

A simple funeral service for Lilly-Sophie was held on April 19 at Adas Israel Congregation at Connecticut Avenue and Porter Street NW. The body was then flown back to Sweden for burial. CAPTION: Picture, Lars Levin and Berit Melin, parents of the baby girl whose death in a hotel bathtub is under investigation.By Margaret Thomas-The Washington Post