FARGO - Alfonso Rodriguez Jr.'s mother says he is a kind, loving son, and a professor and a psychologist say Rodriguez may suffer from the effects of chemical exposure in Red River Valley sugar beet fields.

The three were called as witnesses Tuesday by Rodriguez's attorneys to try to persuade federal court jurors to sentence Rodriguez, 53, of Crookston, Minn., to life in prison instead of death for the killing of University of North Dakota student Dru Sjodin.

Rodriguez showed no emotion during his mother's testimony.

"He's a wonderful son, kind, loving," Dolores Rodriguez told the jury.

When cross-examined by U.S. Attorney Drew Wrigley, she said she found out that her son was abusing drugs and alcohol at about the time he complained of headaches and a swollen head.

"I didn't know about it," she said.

Defense attorneys called two witnesses who testified that Rodriguez may have suffered brain damage from being exposed to DDT and other farm chemicals that were sprayed in the beet field where his family worked. His attorneys say that led to mental and physical problems they believe the jury should consider in sentencing.

Under cross-examination, the two defense witnesses said they could not conclusively link the chemicals to Rodriguez's mental condition.

Donald Ecobichon, a retired toxicology professor, said he looked at a list of farm chemicals that were used in the Red River Valley from 1952 to 1974. He found a "pretty good chance" that Rodriguez was exposed to the toxins while growing up in rural Crookston.

When questioned by Wrigley, Ecobichon said he has no way of knowing the levels of exposure. He agreed with Wrigley that "tens of thousands of people" in the area have been exposed to farm chemicals in the last 50 years.

Ecobichon told Wrigley he could not make a connection between exposure to toxins and "someone's propensity toward violent crime."

Karen Froming, a clinical psychologist from San Francisco who performed psychological tests on convicted Unabomber Theodore Kaczynski among other high profile cases, said her testing of Rodriguez shows that he likely has brain damage that came from exposure to pesticides. She met with Rodriguez in the Cass County Jail in November and May.

Rodriguez fared poorly on vision and smell tests, indicating brain damage from toxins, she said.

"I can't conclusively say one is from the other," Froming said. "But he has significant deficits."

In memory tests, Froming said Rodriguez scored among the top 1 percent on remembering what he sees, but fared poorly on remembering what he hears. Froming said she has seen only three other people with such dramatic differences, and all three were sex offenders.

"It's striking," Froming said.

When cross-examined by Assistant U.S. Attorney Norm Anderson, Froming said the stress of being in prison and facing criminal charges could alter test results. She said Rodriguez could have been faking the answers but said there was no evidence of that.

Froming told Rodriguez's attorney, Richard Ney, that she did not believe Rodriguez was sophisticated enough to falsify the test results. After Anderson asked her if she knew that Rodriguez has read 500 books in prison, including authors like Tom Clancy, Froming said, "I don't know if that speaks to his sophistication."