- NEW: Flags in New Jersey are flying at half-staff
- Investigators are looking at the singer's behavior last week
- Sources: The singer was partying the night before she died
- Hotel surveillance video may help in the investigation
At 11 a.m. ET Saturday, CNN's Piers Morgan, Soledad O'Brien and Don Lemon bring you live funeral coverage on "Whitney Houston: Her Life, Her Music."
Los Angeles (CNN) -- Flags in New Jersey were flying at half-staff Friday to honor native Whitney Houston, but nearly a week after her death, investigators still sought answers about how the singer died.
Investigators were contacting doctors and pharmacies across the country for information on her prescription drug use, trying to determine whether it played a role in her death last week at the age of 48.
Houston's death certificate is only fueling speculation about her death. It lists the cause as "deferred," meaning a determination is delayed pending more information.
The investigation is also looking into the superstar's behavior in her last days. Investigators are aware that Houston partied at her hotel and other venues "even the night before she died," a source close to the death investigation told CNN.
Personnel at the Beverly Hilton in Beverly Hills, California, have said Houston was partying in the bar the night before her death, the source said. A second source said Houston appeared intoxicated as she ordered drinks in the hotel earlier in the week and that she was seen drinking the morning of the day she died.
Investigators are looking at video from Houston's television appearances and at other reports as part of the investigation into her physical state and behavior leading up to her death on Saturday, on the eve of the Grammy Awards, the first source said.
Hotel surveillance video, if it exists, could reveal Houston's activities in the common areas of the hotel, the source said.
The anti-anxiety medication Xanax was among prescription drugs found in the singer's room, the source said. Houston's family members and staff confirmed she used the medication, the source said, but investigators don't know whether she took it the day she died. Xanax is a drug classified as a benzodiazepine, or sedative, but no other benzodiazepines, including Valium, were found in the room, according to the source.
Houston also had a prescription for the antibiotic amoxicillin, the source said, but "if taken as prescribed, it's not going to kill you."
Medicine and pill bottles found in Houston's hotel room are currently undergoing basic testing, but nothing so far indicates anything criminal occurred, the source said.
Officials are trying to speed up toxicology testing, the source told CNN.
The source called speculation any preliminary reporting about family members being told that a deadly mixture of alcohol and drugs led to Houston's death. Investigators do not know what mixture, if any Houston, had in her body.
There have been reports that Houston was found dead in the bathtub of her suite, but the source said that when paramedics arrived, she was in the room, not in the bathroom. "She was lying on the floor, wet, on her back" and had already been removed from the bathtub, according to the source.
"No one official ever saw her in the bathtub or the bathroom," the source said. "The assistant and a bodyguard reported to emergency personnel that Houston was removed from the tub."
Her body was initially discovered by her assistant, Mary Jones, who was often called "Aunt Mary," a family source said earlier this week.
The Mickey Fine Pharmacy and Grill in Beverly Hills is one of the pharmacies subpoenaed as part of the investigation, the source said. The pharmacy did nothing criminal and is not the focus of the investigation, the source said.
One of the prescriptions found in Houston's suite was from Mickey Fine, according to Ed Winter, assistant chief coroner at the Los Angeles County Coroner's office. But "the prescription that came from Mickey Fine is not something that would kill her," Winter has said.
Winter has said that while prescription medication was found in Houston's room, the amount was less than that usually present in overdose deaths.
"I know there are reports that she maybe was drowned or did she overdose, but we won't make a final determination until all the tests are in," Winter said shortly after her death was reported. He ruled out foul play and said there were no injuries to Houston's body.
Houston's battles with drug addiction had cast a shadow in recent years over her impressive singing voice and her talent.
However, a close family friend told CNN on Tuesday that Houston had not used "hard drugs" for several years, although she was taking medication for a throat infection and Xanax or a similar drug for anxiety and to help her sleep. The friend said Houston was also known to have a drink if she went out.
In Newark, New Jersey, fans left balloons, candles and photographs of the singer in front of New Hope Baptist Church, where Houston sang as a child and where her funeral is set to take place Saturday.
Actor Kevin Costner, who starred with Houston in the 1992 hit movie "The Bodyguard," will speak at the private, invitation-only funeral, according to a source with knowledge of the funeral plans.
The ceremony will feature performances by Stevie Wonder, Alicia Keys and Houston's godmother, Aretha Franklin, a Houston representative said. Houston's former husband Bobby Brown and singer Roberta Flack are also expected to attend.
Samuel DiMaio, Newark police director, told reporters Thursday his advice to fans and curious members of the public was to stay home and watch the ceremony on television, as they will not be able to get close to the church.
A perimeter will be set up for four blocks in two directions, and two blocks in the other directions, DiMaio said. The closest the public will be able to get is a staging area two blocks away.
The family is not commenting on Houston's burial location, but her death certificate filed Wednesday in Los Angeles lists it as Fairview Cemetery in Westfield, New Jersey.
CNN's Susan Candiotti, Kareen Wynter, Ross Levitt, Gary Tuchman, Stan Wilson, Alan Duke, Denise Quan and Deb Feyerick contributed to this report.