Doctor Wong Koon-hung said he would have expected to find wood grain patterns or paint smears left on the ornament, or traces of lead on the bat. But no traces of such contact evidence were found, he said.

Wong said he had done controlled experiments using baseball bats bought in Mong Kok to strike tightly clamped lead sheets to attempt to replicate the effect of Robert Kissel's Little League bat striking the base of the metal ornament.

During cross-examination, Wong said he could not produce all his test results since he hammered flat the same metal sheets and reused them, and they now only show the most recent results.

Defense counsel Alexander King SC told the judge: ``We've now heard that the results of earlier tests have been destroyed.''

Kissel, 41, is accused of murdering her husband Robert Kissel on November 2, 2003. The accused testified that on that night, her husband came at her swinging a baseball bat saying, ``I'm going to kill you, you bitch,'' and that she used the metal ornament to protect herself from the blows.

Although she acknowledged in testimony that she struck him five times, she has pleaded not guilty to the murder charge and said she could not remember how she came to inflict the fatal wounds to the side of his head.

The defense has repeatedly suggested that the dent on the base of the metal ornament was caused by the bat's impact.

That was before Wong conducted tests on the possible impact of the bat and the ornament. Tuesday, Wong was re-called to submit ``rebuttal evidence'' in relation to a wooden baseball bat, a defense exhibit, which has been identified by the accused as the one wielded by her husband.

Wong said that while he could not exclude contact between the bat and the ornament, given the controlled experiments, it was doubtful.

When he used one of the bats with ``moderate force'' to strike the sheets of lead, he said, it produced a 1.9 centimeter dent on sheets weighing 2.09 kilograms. On those weighing 2.28kg, he was able to produce an indentation of 1.4cm, he said.

But he added the sheets of lead were ``less resistant to bending'' than the solid metal base of the ornament.

The indentation on the ornament's base measured between 1.4cm and 1.8cm depending on which side.

Earlier in the trial, Wong said he had found the metal base of the ornament to be 1.7kg.

After having caused the indentations, he found wood grains imprinted on the lead sheets and lead smears on the bats, he said.

The sheets also showed ``quite a regular arch shape.''

However, ``I could not find such regular indentation across the base of the metal ornament. Nor could I find wood grain pattern nor paint smears across the metallic structure,'' Wong said.

The two lead sheets bearing regular ``V-shape'' arches and wood grain patterns were shown to the jury.

In cross-examination, King asked Wong to produce the other eight or nine sheets of lead that should be in existence given the record of the tests he had conducted.

Wong said the only available results of the experiments were the two already shown to the jury, since he hammered the sheets flat after previous tests and re-used them.

King said the defense was therefore unable to ``test the science'' of the earlier results.

King showed a picture of Wong's technician striking pieces of lead with a baseball bat. ``What happened to those pieces of lead?'' asked King.

Wong replied that he kept the top layer but he did not consider those underneath to be of importance.

Earlier Tuesday, government DNA profiling expert Dr Pang Chi-ming said ``there was no bloodstain found on the baseball bat'' and that the human material that he found on its handle belonged to neither the deceased, nor the accused, but to another female.

In cross-examination, King asked, ``You would agree, would you not, that not everyone that touches the end of the baseball bat will leave human DNA material that is detectable by testing?''

Pang said that ``if I touch this microphone with my finger, it's possible my human material will not be left on it. But if I held it tightly, and moved it around, I don't believe that my human material would not be left on it.''

He added that if the bat had been kept in a cool area, DNA-bearing material would be preserved longer.

King suggested that after six months, ``you may or may not find material on the article.''

Pang said in the case of the bat, he was able to find human material on it.

``Are you saying then in the history of that bat, only one person has ever held the handle?'' said King.

Pang replied: ``I did not say that.''

The trial was adjourned early Tuesday to give more time for the defense to consider how to continue the cross-examination of Wong.

The trial continues today before Justice Michael Lunn.