Is convicted College Station murderer Stanley Robertson fit to be executed? His attorneys say they'll show he's not over the course of this week.

Tuesday marks the first full day of defense-called witnesses in Robertson's trial, and included testimony from a psychologist who interviewed Robertson concerning his sexual abuse as a child.

Dr. Matt Mendel told jurors that Robertson confided in him a couple of sexual assaults he endured around ages 12 to 14, both by his brother-in-law. Robertson said in the second instance, he was raped by the man, but didn't tell anyone for nearly two decades.

Mendel said Robertson, now 45, already was dealing with the effects of constant teasing because of his family's poverty and his lack of intellect, but the shame and stigma he felt from being abuse only compounded that. Robertson would go on try and kill himself a number of times.

Prosecutors worked to discount Robertson's past as a reason for his crimes, working to get Mandel to note that many people are teased, and some are sexually abused, but not all of those people go on to commit murder.

Defense attorneys conceded their client killed Annie Toliver in the guilt-innocence phase and called no witnesses.

Robertson was found guilty of capital murder in the death of his ex-girlfriend's mother. Toliver was kidnapped from the College Station Walmart in August 2010 and stabbed more than 30 times. She bled to death and was dumped in a Fort Worth parking lot before Robertson led authorities on a chase that ended with him intentionally crashing his SUV into an officer's patrol car.

Monday, the defense began calling witnesses, most of them being siblings of Robertson who testified to the poverty that faced the family as they worked and lived on farm fields in Alabama. The defense offered that pesticides constantly sprayed on the fields could have altered Robertson's mental state.

The Diagnostic Statistical Manual of Mental Disorders notes three things must be shown to prove mental retardation is present in a person:

- an IQ below 70, or below 75 within a margin of error
- clear deficiencies in adaptive behavior
- the low IQ and deficiencies clearly showing up before the age of 18

The defense says they'll show Robertson has the disorder, and is ineligible for the death penalty.

An Alabama public school official testified Monday that Robertson took special education classes. However, she also noted that Robertson's school records were marked showing him to be a level above the district's mental retardation status.

The State of Texas must show Robertson is a clear danger to others, that there are no mitigating circumstances that would keep him from being executed, and that he is not mentally retarded. Otherwise, the death penalty they seek is not an option. Instead, Robertson would be sentenced to life in prison without possibility of parole.

Court will resume Wednesday at 2:00 p.m. when a defense witness arrives from out of state.