FORT MYERS, Fla. -- A southwest Florida man is in custody after his girlfriend, her teenage daughter, the couple's toddler and their dog were found dead at their home.

Jail records show that 27-year-old Patrick Sean Carlopoli was being held Monday on multiple charges. Local media outlets report that Lee County deputies responded early Sunday morning to a 911 call from Carlopoli at Iona Lakes Apartments in Fort Myers.

Lee County Sheriff Mike Scott described the scene at the apartment as a "gruesome" crime scene, reports CBS affiliate WINK.

"I often tell people when I speak publicly that we're in the business of whatever happens next," Scott said during a Monday morning press conference. "And whatever happens next is many times unpredictable, unpreventable, and frankly unthinkable. The events of early Sunday morning were all of the above, with an underscore on unthinkable."

Get Breaking News Delivered to Your Inbox

An arrest report says Carlopoli directed deputies into an apartment, where they found 37-year-old Tammy Modlin and 16-year-old Montana Modlin dead on a bed with a firearm between them. The deputies also found 3-year-old Jeanne Carlopoli and a dog fatally stabbed.

"Patrick had visible blood splatter on his body and clothing," an arrest report said, WINK reports. "Patrick told deputies 'they are in there,' pointing inside the residence...deputies detained Patrick, who made a spontaneous utterance that he shot his wife."

The report said that Carlopoli told deputies that he shot his "wife," though officials say the couple wasn't married.

Jail records didn't list an attorney for Carlopoli.

WINK spoke with a neighbor of the family, Leslie Hansen. She said she was regretful when she heard about the killings.

She told WINK she would see Jeanne Carlopoli looking through one of the windows every time she walked by.

"She was a beautiful little child and innocent and she didn't deserve what happened to her," she said.

Jeanne Carlopoli. CBS affiliate WINK

Hansen said she felt slightly responsible for what happened because it appeared Jeanne needed help when she looked through the window recently.

"She looked like there was something wrong," she said. "She was always in the same pajamas, her hair was never combed. Looked dirty."

Hansen said she wished someone would have called to help.

"I know a lot of us thought about it," she said. "I don't know why none of us did but maybe if we had, she would still be alive."

Jeanne's fourth birthday is Feb. 28.