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By Daniel Arkin and Tim Stelloh

A man who had been sought in the gruesome deaths of five people, including his own daughter, in Modesto, Calif., was arrested Sunday, police spokeswoman Heather Graves said.

Graves said that Martin Martinez, 30, also had a "past relationship" with one of the victims, all of whom were female. Three children — ages six months to six years — were among the dead. At least one of those girls was his daughter, Grave said.

Martinez was booked into Santa Clara County jail on suspicion of murder and was expected to be returned to Modesto, officials said. Police aren't releasing information about a motive or cause of death at this time, Graves said.

Authorities have released few details about the investigation, though police said Saturday they were treating the deaths as a homicides.

The killings shocked residents of the quiet neighborhood in the city of about 200,000 people. Shawna Avery, who lives a street behind where the bodies were discovered, told NBC affiliate KCRA that it was quiet all day Saturday.

"This would never happen here. You would not expect this," she told the station.

Phil Helsel contributed.