Police were searching for a motive in the deaths of four young children whose remains were found in the family's townhouse Monday afternoon along with the hanged body of their father. The children's mother was missing and police said Tuesday they were concerned for her well-being.

"We are doing everything we can to try to locate her and of course, first and foremost to verify that she's OK," Frederick police spokesman Lt. Thomas Chase said.

The children — girls ages 9, 4 and 1, and a 3-year-old boy — were found in beds beneath sheets and blankets that were pulled over their heads. The cause of their deaths was not known; autopsies were set for Tuesday in Baltimore.

Click here to visit FOXNews.com's Crime Center

Their father, Pedro Rodriguez, 28, was found hanging by a yellow nylon rope from a second-floor bannister, Chase said.

The children's mother, Daysi M. Benitez, 25, also lived in the townhouse but she hadn't been seen by neighbors and co-workers at a local restaurant for about a week and a half, Chase said.

Chase said police don't have any suspects in the deaths of the children. When asked if they believe the father killed them, he said that was a theory they were pursuing.

"You've got four dead people, and a guy that hung himself. That leads you to one possibility," he said.

The bodies were discovered after a Hillcrest Elementary School community liaison concerned about the two oldest children's' absence from school for several days called police, authorities said. Officers entered through an unlocked ground-floor window Monday afternoon and found the bodies in different rooms of the three-bedroom home.

"It was not like them to miss school," said Marita Loose, a Frederick County schools spokeswoman.

Jose Lopez, 34, said he had rented a room in the townhouse for about two months a year and a half ago. When he lived with them, the couple seemed happy, he said.

Real-estate records show that Rodriguez and a Deysi M. Benitez bought the home in August 2005 for $195,900. Chase said the different spelling of Benitez's first name in a police press release came from police records.

The family had emigrated from El Salvador to the United States, police said.

Police had been called to the townhouse three or four times in the past six months, neighbor Nathaniel Harris said.

"Everyone in the neighborhood is shocked," Harris said. "This is a nice area."

Another neighbor, Rebecca Reckley, said Rodriguez worked at a Toys R Us distribution center in Frederick and Benitez worked at an Outback Steakhouse. She worked nights and he worked days, she said. However, Kathleen Waugh, a spokeswoman for Toys R Us said they have no record of Rodriguez working for their company.

"He just seemed like an awfully nice man," she said. "He just seemed to really care about his children, so you can't fathom something like this would happen."

Lopez said that when he lived with the family, Rodriguez had a second job at a Uno Chicago Grill restaurant.

Managers at Outback and Pizzeria Uno refused to comment.

Frederick is about 50 miles northwest of Washington.