CHATTANOOGA, TN (WRCB) -- A Chattanooga woman is pleading for answers in her sister's death. Police found Deborah Underhill's body near the Tennessee River last Friday. Investigators are calling her death suspicious. Her sister says she was murdered.

"I will not sleep or sit or close my mouth until I find out who did this to my sister," says Karen Searle.

For Karen Searle, the pain is almost too much to bear. She says too many questions surround the death of her sister, 57-year-old Deborah Underhill.

"I'm wondering why she didn't call me Thursday when she left that AIM Center, because she always called me, and I know she always wanted me to come get her. And I always went and got her. And I would have went and got her," she says, holding back tears.

Deborah was last seen around 9:30 Thursday morning at the AIM Center in downtown Chattanooga. More than 24 hours later, her body was found Friday evening near the Brown's Ferry Marina.

"She had some injuries that are just suspicious in nature," says Nathan Hartwig, with the Chattanooga Police Department.

Karen says in recent years her sister has dealt with mental issues but knows in her heart of hearts there is more behind Debbie's death.

"They know Debbie didn't do this to herself. And I knew my sister didn't leave her boys. She has two boys and two grandbabies and she wouldn't have left them."

After many sleepless nights, she is begging for help.

"Please, God in heaven, if anybody saw her anywhere or think they did, or think they know anything, please let the investigators know," says Searle.

She says she is at peace, knowing her sister is in a better place, and as hard as it is, she does not hold any ill-will for who is responsible. She just wants answers.

"This person can be forgiven. Through God in heaven, He'll take care of that."

Deborah was laid to rest Wednesday.

The medical examiner's office has not yet finished the autopsy report, only calling it an undetermined death with 'suspicious injuries.'

If you have any information that can help solve this case, call the Chattanooga Police Department at 423-698-2525.