Three of six women Robert William Pickton is accused of killing may have died of drug overdoses, one of his lawyers suggested on Monday.

But forensic toxicologist Heather Dinn, who was asked to test tissue from the remains of Sereena Abotsway, Andrea Joesbury and Mona Wilson for drugs, rejected defence lawyer Richard Brooks's suggestion.

The trial, in B.C. Supreme Court in New Westminister, began in late January. Pickton has been charged in the deaths of Abotsway, Joesbury, Wilson, Marnie Frey, Georgina Papin and Brenda Wolfe, among missing women from Vancouver's Downtown Eastside.

In all, he is accused in the deaths of 26 women. He has pleaded not guilty to all the charges. Another trial on the 20 other counts will be held later.

Test results revealed

Jurors were told that Joesbury's remains tested positive for an antihistamine, methadone and cocaine. They also tested positive for a substance created in the body by the liver when a person consumes alcohol and cocaine together. 

Abotsway's remains tested positive for cocaine and Wilson's remains contained traces of Valium, cocaine, methadone and the same substance created by the body when alcohol and cocaine are mixed. 

Brooks then suggested the levels of some of these drugs found in the tissues of these women were within a fatal range, and it was possible each one died of a drug overdose. 

But during a heated exchange with Brooks, Dinn said that that was an incorrect conclusion.

Dinn said she could only run tests on the tissue from the hands, head and feet of the women.

She said you can't compare toxicity levels found in tissue with levels found in the liver, adding that the scientific research on toxicity levels has been done on blood and liver samples.

'Interpretation cannot stand alone'

Dinn said Brooks was "comparing apples to oranges.

"Because there is no literature behind it, to draw that interpretation. Interpretation cannot stand alone. It must be supported by data in the literature and the data must be relevant to the specimen examined," Dinn told jurors.

The fact that the tissue submitted to her was in varying states of decomposition made the task even more difficult, Dinn also testified.

She did testify that because of the levels of cocaine in the tissue, two of the women may have used cocaine within 24 hours of their death.

Dinn said she was also asked to look for the presence of methanol and ethylene glycol — common components in windshield-washer fluid and radiator coolant. 

A forensic chemist confirmed that a syringe recovered from Pickton's trailer contained a mixture of methanol and water.

Early in the trial, jurors heard on the videotape of Pickton's interrogation that an acquaintance of the B.C. pig farmer said Pickton told him a good way to get rid of someone was to inject them with windshield-washer fluid.

But none of the remains tested positive for methanol or ethylene glycol, Dinn testified.