At issue is whether it was an accident or murder. If convicted of murder, Mallard could face life in prison, reports CBS News Correspondent Bob McNamara.
Closing statements in Mallard's trial were to begin Thursday morning.
"It is believed by many that this has been a trial from the beginning of punishment, not guilt or innocence," said Court TV reporter Jean Casarez said on CBS News' The Early Show. "It is believed she will be convicted of something."
The biggest question, the Casarez said, will be answered by the penalty phase of the trial.
Two medical examiners — one testifying for the prosecution, the other for the defense — gave slightly different accounts of Biggs' condition and how long he may have lived after being hit by a car and left in the windshield.
The only defense witness was Vincent Di Maio, chief medical examiner for Bexar County, and the defense rested Wednesday afternoon after his testimony.
Di Maio said the 37-year-old Biggs was instantly knocked unconscious after his head hit the windshield and probably didn't speak inside the car, where he likely lived for one or two hours.
"He had to have been knocked out. I can't see any other way," Di Maio told jurors. "If you knock a windshield out with your head, you're going to be unconscious."
Other than the consciousness issue, Di Maio backed up many of the conclusions made by the prosecution's star witness, Dr. Nizam Peerwani, the Tarrant County medical examiner who performed Biggs' autopsy, reports L.P. Phillips of CBS Radio station KRLD.
Mallard did not testify in her own defense, but Casarez told CBS News Early Show co-anchor Hannah Storm that could change.
"There's a possibility that they will put her on the stand in the penalty phase because she does not have a criminal record and she's led a very clean life," Casarez said.
Mallard told police that after parking in her garage, she apologized to Biggs as he moaned.
Before the state rested its case just after noon Wednesday, the victim's son told jurors that his father was a self-employed brick layer who took medication for bipolar disorder and mild schizophrenia.
Brandon Biggs said he regularly saw his father, who lost his truck and house after loaning money to a girlfriend nearly two years before his death. He said the two lost touch in 2001.
"Although he didn't have many friends, he was very friendly, and he was very, very loving," said Brandon Biggs, 20.
"It was such compelling testimony for the prosecution because this is the only living, breathing reminder of Gregory Biggs and he was a very eloquent young man on the stand," said Casarez.
The prosecution's evidence — photographs, expert witnesses — also seems to be affecting the jury, said Casarez.
Di Maio, who reviewed the Tarrant County medical examiner's autopsy report, said Biggs also had problems breathing because his head was on the floorboard and his torso was lodged between the passenger seat and dashboard. He said he did not know if Biggs' legs were protruding outside the car.
Peerwani testified earlier Wednesday that Biggs probably died about two hours after he was hit. Biggs' injuries would not have prevented him from moving his hands and talking, and he was not asphyxiated while lodged in the car, Peerwani said.
Biggs' right arm, right thigh bone and right shin bones were broken, the lower part of his left leg was nearly amputated, and he had deep cuts in his torso, Peerwani said.
"He was obviously in severe, excruciating pain," Peerwani said.
Di Maio and Peerwani both said that despite the injuries, Biggs could have survived with medical treatment because the crash did not cause injuries to his brain or other organs.
Biggs' body was found Oct. 27, 2001, in a park. Mallard's former lover, Clete Jackson, and his cousin Herbert Tyrone Cleveland have pleaded guilty to tampering with evidence for helping dump Biggs' body.
Jackson was sentenced to 10 years; Cleveland, nine years. As part of the plea bargain, both agreed to testify at Mallard's trial, but prosecutors never called Cleveland.
Earlier this week, Mallard pleaded guilty to tampering with evidence and faces a sentence of up to 10 years on that charge.