SUNRISE, Fla. -- Police say an 18-year-old woman used her cell phone to call 911 for help Monday night, but by the time officers arrived, she had been killed.

Sunrise police said when officers arrived at the apartment building at 5990 N.W. 19th St. just after midnight, Christine Myers was lying dead in a hallway.

Police arrested 26-year-old Edward Mosie Howard on Tuesday.

Investigators said Myers and Howard knew each other, but investigators said they don't know a motive for the killing.

Howard made his first court appearance Wednesday. He is being held without bond on murder and sexual assault charges. Police said he also has a no-bond hold for a probation violation.

Police said that Howard is a "career criminal," with numerous arrests dating back to 1994. Investigators said he has been imprisoned several times for a variety of crimes. He was released from prison two months ago.

During Howard's bond hearing, prosecutors said that there is an eyewitness who recounted seeing Howard "on top of" Myers. Police said that Howard told officers that he was "sorry she had to die."

Police said that there were marks on Myers' body indicating that she had been strangled.