Los Angeles (CNN) -- Whitney Houston's mother and daughter attended an emotional private viewing Friday, hours ahead of the pop singer's funeral in Newark, New Jersey.
Cissy Houston and Bobbi Christina Brown were joined at the funeral home by music producer Clive Davis, credited with discovering a young Whitney Houston in the early 1980s.
Flags in the state flew at half-staff Friday to honor Houston, 48, a New Jersey native. She died February 11 in Beverly Hills, California.
Actor Kevin Costner, who starred with Houston in the 1992 hit movie "The Bodyguard," will speak at the invitation-only service Saturday at New Hope Baptist Church, according to a source with knowledge of the funeral plans.
The ceremony will feature performances by Stevie Wonder, Alicia Keys and close family friend Aretha Franklin, a Houston representative said. Houston's former husband, Bobby Brown, and singer Roberta Flack also are expected to attend.
Franklin, in concert Friday night at Radio City Music Hall in New York, told the audience, "It is my sincere hope to sing something to uplift our heavy hearts this evening." Among her selections were "Jesus Loves Me" and "Amazing Grace."
"We will always remember her kindness, her grace, her smile and her dynamic performances, but she's moved on up just a little bit higher now and we don't wonder where she is," said Franklin.
Houston's close friend, reality TV star and singer Ray J, released his first statement about her death, saying he feels an "emptiness" at her loss.
"What my heart feels cannot be expressed in words," said Ray J, who was Houston's frequent companion in the days before she died. "The world lost an icon, but I lost my close friend. Nippy, I miss you so much! You were so happy and full of love. Your smile will live in my heart forever."
Friday night's 43rd annual NAACP Image Awards, broadcast on NBC, featured a video and musical tribute to Houston.
Gospel singer Yolanda Adams, backed by a small choir, sang "I Love the Lord," which appeared on the soundtrack of "The Preacher's Wife," a 1996 film that starred Houston. The show ended with Kirk Franklin and others singing "The Greatest Love of All."
Meanwhile, investigators seeking answers about how the singer died were contacting doctors and pharmacies across the country for information on her prescription drug use. They are trying to determine whether it played a role in Houston's death.
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 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 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.
Ed Winter, assistant chief coroner at the Los Angeles County coroner's office, 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.
CNN's Jason Carroll, Susan Candiotti, Sunny Hostin, Meghan Rafferty, Kareen Wynter, Ross Levitt, Gary Tuchman, Stan Wilson, Alan Duke, Denise Quan and Deb Feyerick contributed to this report.