A registered sex offender fatally shot a 17-year-old girl he had been harassing, then killed himself after an hour-long standoff with police Saturday, authorities said.

Police had been investigating 42-year-old Scott David Uslan's relationship with Brittany Carleo for several months, but did not have probable cause to arrest him until Wednesday after he started making harassing phone calls to the teen, police spokesman Rob Vega said.

Uslan posted bond and was released from jail Thursday. He entered the smoothie cafe where Carleo worked with a gun around 9:15 a.m. Saturday, police said.

"Unfortunately this mad man was not kept behind bars where apparently he should have been kept, and unfortunately we have a young girl who is now dead," Vega said.

Two other cafe employees escaped out the back.

Uslan had been obsessed with Carleo since she started dating his son two years ago, and the teen eventually sought a restraining order against him, family members said.

"If he couldn't have her, no one else could have her," her aunt, Barbara Martin, told The Tribune for Sunday's editions.

Uslan was registered as a sexual offender in Florida because of a previous conviction of providing obscene material to a minor.