SANTA CLARA COUNTY (KRON) — A toxicologist took the stand Wednesday during the penalty phase of the murder trial to address whether exposure to harmful pesticides might have affected Sierra LaMar’s convicted killer.

Antolin Garcia-Torres, 26, was convicted May 9 of the 2012 murder of 15-year-old Sierra LaMar as well as the attempted kidnappings of three women in 2009.

The penalty phase of the murder trial continued Wednesday as the jury decides whether Garcia-Torres will get the death penalty or life in prison.

Garcia-Torres’ defense is arguing that he may have been exposed to harmful pesticides, like perchlorates and “possibly” mercury.

Dr. Andres Lugo, a toxicologist, is addressing the possibility that Garcia-Torres was exposed to and affected by harmful pesticides at an early age.

The convicted killer grew up in a shack in the middle of the San Martin strawberry fields where his Mexican-born parents picked fruit.

On Monday, his mother, Laura Torres, testified about her exposure to pesticides when she worked in fields while she was pregnant with Antolin.

Dr. Lugo said that research shows farm workers bring chemical residue home on their clothing and that pregnant women and children are at risk.

KRON4’s Rob Fladeboe is in the courtroom with the latest: