Jennifer Mejia should have been at her prom Wednesday. Instead, her sister could only imagine Jennifer in her long, flowing prom dress.

One of Lesly Mejia's last images of her sister was posing in her dress Saturday night.

The next day, on a Sunday morning, Jennifer, 17, was among four victims of the Medford pharmacy slayings, shot to death by a lone gunman who robbed the store of prescription painkillers.

"She was really like an angel on earth," Lesly said of her sister. "She was perfect."

Lesly Mejia, 16, was leaving her Medford home to attend Jennifer's wake Wednesday when she learned police had made an arrest in the murders.

But the arrest -- a Suffolk County police source identified the man as David Laffer, 33, of Medford -- left her hollow, she said.

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"It's not going to bring back my sister," Lesly said, speaking publicly for the first time since her sister's death. "God will know what to do with him."

Lesly described her sister as bright, hardworking and as someone "who always talked about helping other people."

Jennifer had worked at the Medford pharmacy for about two years, her sister said. She recalled that Jennifer sent her first paycheck from the store to their grandmother in El Salvador.

Her sister, Lesly said, had a habit of putting other people first and wanting everyone to feel special.

On Sunday morning, when Jennifer left for work, she had just enough time to wish their father a happy Father's Day. Then she wished her mother happy Mother's Day.

"She was just like that," Lesly said. "She didn't like leaving anyone out. She had a really strong heart."

On the way to the prom Wednesday, some of Mejia's classmates, young men in suits and girls donning lavish prom dresses and gowns, stopped at Haven Drugs -- the site of the shooting -- in her memory.

They brought the corsage Mejia would have worn, placing it on the pavement in front of the drug store along with the flowers, candles and cards that had been left at the makeshift memorial.

The students took pictures in front of the memorial, while holding a large photo of Mejia, tears streaking the face of one girl as she broke down remembering Mejia.

Mourners Wednesday afternoon packed a Patchogue funeral home for the high school senior's wake.

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The Robertaccio Funeral Home parking lot was filled and vehicles packed an overflow lot and the streets for the 2 p.m. wake. Mourners streamed in and out of the funeral home.

Carrying a prayer card with Jennifer's photo, her Bellport High School classmate, Jenna Lundberg, 17, said through tears she was "so happy" a suspect was captured in her friend's death.

Inside the wake, she said, it was quiet and mourners were emotional.

Her mother, Alice Lundberg, 50, said: "I'm sick to my stomach. She should be getting ready for the prom."

With Gary Dymski and Jeremy Schneider