FORT WORTH, Texas (AP) _ A judge declared a mistrial Monday in the wrongful death lawsuit against millionaire Cullen Davis after jurors said they couldn't agree whether he shot four people, two fatally, at his hilltop mansion 11 years ago.

The mistrial came in the fourth day of deliberations and perpetuated one of the state's most famous murder mysteries that has spawned books and fascinated Texans for more than a decade.

''Cullen Davis killed those people and he got by with it. It tears me apart. It really tears me apart,'' said the tearful jury foreman, Kenneth Pool.

State District Judge Claude Williams declared the mistrial after reopening arguments earlier in the day in an attempt to break a 8-4 jury deadlock, reportedly in the favor of the plaintiffs. A 10-2 verdict is needed in civil trials.

Jurors said they couldn't agree whether Davis should have to pay the $16.5 million in damages sought by his ex-wife, Priscilla Davis, and her former husband, Jack Wilborn, for the death of their daughter, Andrea, 12.

Davis was acquitted of murder in the case 10 years ago, but that had no bearing on this case, which went to trial May 26. Pool said the jurors ''went on reasonable doubt like a criminal case,'' instead of basing their decision on the preponderance of evidence as required in a civil trial.

Mrs. Davis told reporters, ''I don't feel like justice was done. I will go to the grave knowing that Cullen Davis killed my child.''

As Davis' supporters cheered and surrounded him, the 53-year-old industrialist said, ''I'm glad it's over. I'm disappointed I didn't win it the way I wanted to,'' which he said would have been via a clear-cut verdict in his favor.

Wilborn said he was bitterly disappointed with the outcome. ''It hurts.'' He said he did not know whether he would pursue his civil lawsuit, and his attorney, John Collins, said, ''We need to go home and think about it.''

Mrs. Davis' attorney, Bob Gibbins, repeated his earlier vow not to pursue the matter. ''I will keep my word we will not come back, because as I said, there will be no tomorrow. It will be now or never.''

According to eyewitness testimony, a black-clad gunman wearing a crude black wig killed the child and Mrs. Davis' boyfriend, Stan Farr, 30 on the night of Aug. 2, 1976. Mrs. Davis was wounded, as was a friend of hers, Bubba Gavrel.

Gavrel, then 22, was partially paralyzed by in the shooting, but Beverly Bass, his teen-age date that night and now his wife, escaped unharmed.

A civil lawsuit filed by Farr's estate is set for a September trial.

Miss Bass, Gavrel and Mrs. Davis testified that Davis was the gunman.

During the reopened arguments, plaintiffs' lawyer Bob Gibbins appealed to the panel to consider again the eyewitness testimony.

''Three eyewitnesses said Cullen Davis was the one who did this,'' Gibbins said. ''How much stronger can you get?''

Davis' lawyer, Steve Sumner, urged jurors to ''stand by your convictions'' and not be stampeded into ''compromising your integrity.''

The jury has been split in favor of the plaintiffs since last week, according to sources who asked not to be identified.

Mrs. Davis and Wilborn contended in their consolidated wrongful death lawsuits that Davis was the man in black who killed two and wounded two in the massacre at the $6 million mansion the defendant once called his ''dream home.''

It was their daughter, Andrea, who first encountered the man in black. He shot her once through the chest and left her to bleed to death on the floor of the mansion basement.