The opening statements heard in county Superior Court in El Centro came after a weeklong effort to seat a jury, and there were indications Friday it could take weeks to present evidence.
The accident that killed Michelle occurred just before midnight Oct. 7. She and two friends were standing by a golf cart that was stopped on Wheeler Road when the van driven by Mostrong struck the cart, Michelle and Welter.
Another friend, Charlotte Lang, jumped out of the way and was uninjured.
Michelle was thrown 107 feet, according to authorities.
Mostrong was arrested Oct. 8 after he turned himself into the California Highway Patrol office in Imperial.
In his opening remarks, Robinson told the jury Mostrong and others were in the Superstition Mountains to attend a "keg" party.
Robinson said Michelle and her friends were not there for that party.
Robinson further told the jury he will present witnesses who will testify they saw Mostrong drinking beer and smoking pot.
When Mostrong "decided to get in his van and go into the desert he began a chain of events that led to this tragedy," Robinson told the jury.
Robinson said he will present evidence others were in the van with Mostrong and one of those asked to be let out or for Mostrong to slow down because he was driving erratically.
Robinson said he will present a witness who will say he saw a light while Mostrong was driving along Wheeler Road, and that the witness told Mostrong to slow down, but he kept his van in fourth gear.
After Mostrong's van struck Michelle, Robinson contended, Mostrong drove for another 200 feet before stopping.
Robinson contended Mostrong and the others got out of the vehicle but did not go to aid Michelle or her friends. Instead, Robinson contended, Mostrong got back into the vehicle and drove away.
He did not turn himself into the California Highway Patrol until 17 hours later, and at that time his blood/alcohol level was .00. However, Robinson said he has evidence that will show Mostrong did have marijuana in his system.
Robinson asked that the jury find Mostrong guilty of gross vehicular manslaughter, driving under the influence and hit-and-run.
In Espinosa's opening remarks, he asked that the jury deal with this case in an "unimpassioned" manner.
"Cases like this that involve the death of a human being are passionate cases," he told the jury, adding they need not let the passion of the case sway them.
"Our sympathies might be there, but our prejudice cannot," he said.
Espinosa stated the golf cart was in the north lane of the dirt road 13 feet from the curb in the line of oncoming traffic.
He said he had an important point to make that was crucial to Mostrong's state of mind.
"Blake Mostrong, at the age of 10, walked into the house to find his mother's body dead on the bed," Espinosa said.
He added, "It's important to know the tragedy and trauma that caused him and continues to cause him and how it affected him on the night in question."
Espinosa then told the jury there were points Robinson had not told them. He told the jury it was not told Michelle had been drinking the day she was killed and had a blood/alcohol level of .05, and that Welter had a blood/alcohol level of .07.
Espinosa said the California Highway Patrol officer handling the case had made mistakes in his report, and that those mistakes had been corrected, and the originals had been destroyed before he had a chance to review them.
Espinosa told the jury he will have witnesses who will say the golf cart did not have its lights on and that Mostrong had not been drinking or smoking marijuana.
He further contended Mostrong, who was in shock, did not drive away from the scene, but rather was placed in the van by another individual and that that individual drove Mostrong to get help.
Espinosa did not name that individual.
He said at some point the van suffered a flat tire and the individual and Mostrong walked 17 miles to Imperial.
Espinosa ended his statements by saying the prosecution must prove Mostrong had an "I-don't-care attitude." He said his client did not have such an attitude.