It's possible that three people still missing in central Ohio have been killed, a sheriff conceded Monday, a day after the 13-year-old girl who disappeared along with them was rescued from the home of a man later charged with kidnapping.

Authorities still want to remain optimistic that 32-year-old Tina Herrmann, her 10-year-old son, Kody, and Herrmann's friend, 41-year-old Stephanie Sprang, are alive, Knox County Sheriff David Barber said at a news conference.

Investigators searched a lake for signs of the three near a house where 13-year-old Sarah Maynard was found in the basement and where Matthew J. Hoffman, 30, was arrested. Maynard has been released from a hospital and is staying with relatives, the sheriff said.

"She is a very brave little girl," Barber said. "Under the circumstances, a 13-year-old girl being held captive for four days by a total stranger ... I would call her the epitome of bravery."

Unlike previous days, the sheriff declined to describe the investigation as a missing-persons case, referring to it as "an investigation into the recovery of three people."

The shift in tone was owing to the amount of blood found at the home, the fact that only Maynard was found with the suspect and because apparently no one has seen her mother, brother and the other woman.

"We still would like to retain a hopeful attitude, but we have to be realistic," Barber said.

It was unclear whether Hoffman knew either of the missing women, the sheriff said earlier. He did not say what led investigators to the two-story tan-sided house about 40 miles north of Columbus but said more charges are expected against Hoffman.

Foundation Park, a public park with a lake a few blocks from Hoffman's home, was closed Monday, initially by Mount Vernon police because an officer patrolling overnight had found what he thought was bloody clothing potentially related to the investigation, police Capt. George Hartz said. But tests did not find any human blood on the clothing, he said.

The city reopened the park at midmorning, only to have it closed again a half-hour later by county and state authorities so they could search the lake with a boat equipped with sonar, Hartz said. He did not have other details on the lake search.

Hoffman's neighbor, Dawna Davis, told Fox News that he frequented the park, which was once a gravel quarry and now has three lakes where people fish. 

"I can't believe I didn't hear anything so close," said Davis, 35, who lives next door to Hoffman.  

Hoffman was being held in the county jail, where personnel would not comment on whether he had an attorney. A bond hearing was tentatively scheduled for 1:30 p.m. Tuesday, the Mount Vernon Municipal Court clerk's office said.

Herrmann, her children and Sprang, disappeared Wednesday from Herrmann's home in nearby Howard. Barber said DNA testing on blood found in that house was expected to begin Monday.

Authorities believe the girl had been "under the control" of Hoffman since Wednesday, when she and her brother last attended school, the sheriff said. He did not know if Hoffman was connected to either Herrmann or Sprang, but said he is not the ex-boyfriend of either woman.

"At this time, whether he's connected to the family or whether he connected himself to the family ... a lot of that remains to be seen as the investigation continues," Barber said earlier.

Authorities blocked off about a half-block on either side of the home as they investigated Sunday afternoon, keeping people from entering or leaving about a half dozen homes. But later in the afternoon, the only sign of investigative activity was red and white evidence tape sealing the front door of the home.

The house with green shutters and front door and a large television antenna on the roof sits in a lower-middle-income neighborhood with two bars within a block. Holly grows through the weathered slats of the porch. A sheet covered one window, and blinds were pulled down on the rest.

Davis said she told her children to stay indoors when he was out. She said he moved in alone about a year ago and that a girlfriend lived with him temporarily with her son until about a month ago.

"He would sit and listen to us up in a tree. He had a hammock and he would sit there and listen to us," she said. "He was just different. He was very different."

Davis said Hoffman did tree trimming work and had built a fire Wednesday night in his backyard, where there was a mound of ashes Sunday with tree parts on it. She said he walked to Foundation Park almost every day and was a "nature person" who collected leaves.

Herrmann was reported missing Wednesday when she did not show up for work at a local Dairy Queen. Barber has said blood indicating an injury had been found in her home, where Sprang's vehicle was in the driveway.

Herrmann's pickup truck had been found Thursday night near the Kenyon College campus, leading to a lockdown at the school.

The Associated Press contributed to this report