Wierd, 6 killed in Memphis without explanation.

Four adults and two children were found dead in a home Monday in Memphis, Tennessee, authorities said. Three other children were wounded.

A neighbor told CNN he had heard shots at the home Saturday night.

The four dead adults were shot and the two dead children were stabbed, sources told CNN affiliate WMC-TV.

At least one of the wounded children also was stabbed, police told the Commercial Appeal newspaper.

"I heard about six or seven shots," said Wayne Bolden, a landscaper who said he lives across the street from the home where the killings occurred. "I did not call the police because you always hear shooting in this neighborhood. Now I wish I would have called."

He said he did not see any movement at the home the next day -- the two cars, a van and a passenger car, never moved.

Monday he saw many police cars at the home and heard about the killings, he said.

Memphis Fire Department spokeswoman Melanie Young said firefighters responded to a 911 call at a home at 6:11 p.m. Monday and found the bodies and wounded children.

A 7-year-old boy, a 10-month-old girl and a 4-year-old whose gender wasn't immediately known were taken to Le Bonheur Children's Medical Center.

The Commercial Appeal newspaper said one child was upgraded to stable condition late Monday, another was upgraded to critical and the third was still in extremely critical condition.

Police do not know what was behind the violence, the newspaper reported.

"We just don't know the motive or cause of death, but we do have four adults and two children [dead]," Memphis police Lt. Jerry Guin told the paper.

Rob Robinson told the Commercial Appeal that he was the landlord for the brick, single-family house that rented for $550 per month.

"They were very nice, very polite to me," Robinson told the paper of the residents.

"It's kind of surprising, actually. I've never had any trouble with them, no damage to the property. They paid their rent and even helped with repairs and stuff."

Neighbor Leo Baker told CNN affiliate WMC-TV he has lived nearby for 10 years but did not know the residents of the home.

"It's sad you come home to find out something like this has gone on," Baker said. "It's kind of sad, and scary too."

Video footage showed emergency vehicles on the scene, with people embracing in rainy weather outside police tape surrounding the home.

"I've been on a scene where there were one or two or three [victims], but I don't remember anything this large," Guin told the Commercial Appeal.

The newspaper reported that the shooting appeared to be the city's deadliest mass killing since 1973, when 28-year-old David Sanders randomly shot and killed five people before being shot dead by police.

In 2000, police said firefighter Frederick Williams confessed to a shooting in Memphis in which four people were killed -- his wife, a sheriff's deputy and two fellow firefighters.