Instructions to the jury in the trial of Alberto Alvarez, accused of murdering East Palo Alto Police Officer Richard May in January 2006, will include a modern-day admonition: No tweeting.

That instruction to refrain from the website Twitter was one of several decisions San Mateo County Superior Court Judge Craig L. Parsons and attorneys for the defense and prosecution worked out on the opening day of Alvarez's capital-punishment trial Tuesday.

Alvarez, 25, is charged with first-degree murder with special circumstances and could be given the death penalty or life in prison without the possibility of parole if convicted. He allegedly shot May to death after the officer responded to a call about an argument at a University Avenue restaurant in East Palo Alto.

On Tuesday, Parsons ruled on jury-selection criteria and left open the possible admission of some evidence at the end of the trial that alleges Alvarez is a member of the Sacramento Street Gang.

In March, Parsons blocked evidence of Alvarez's alleged gang affiliation. He reaffirmed that ruling on Tuesday, saying the alleged gang connection cannot be presented as a motive. But he would consider in a separate hearing later whether prosecutors can use the argument during rebuttal at the end of the trial, he said.

Defense attorneys are expected to present expert witnesses to testify that Alvarez suffers from post-traumatic stress disorder (PTSD) that could have affected his actions.

Eric Liberman, one of two defense attorneys, has previously said he will present evidence that May operated outside the scope of his duties, allegedly beating Alvarez with a baton, and fired a shot at Alvarez as the defendant ran away.

But Steve Wagstaffe, San Mateo County chief deputy district attorney, argued that if the defense is allowed to present the PTSD argument, the prosecution should be allowed to present gang-affiliation evidence in order to draw a distinction between Alvarez as an innocent victim of a violent world and bringing violence upon himself.

Alvarez "sought out gang activity. He was not just a victim of a violent world, but he was one of the active participants in the violent world," Wagstaffe said.

Parsons ruled he will conduct separate hearings during the trial regarding the scope of the expert psychiatric testimony.

Questionnaires given to potential jurors will address their feelings about the death penalty, the defendant's purported gang membership, their feelings about minorities or Hispanics, and their exposure to pretrial publicity, Parsons said.

But those questions will be asked of potential jurors only when questioned individually -- but not during the group-questioning phase of jury selection, he said.

"We want to seek to ensure that we don't have jurors tainting other jurors," Parsons told attorneys.

Alvarez, looking thinner and paler than in his arrest photos, sat passively in red jail clothing, shackled at the waist and ankles.

Jury selection in Alvarez' trial was to begin March 23. But the slayings of four Oakland police officers on March 21 were so similar to the May case that San Mateo County Superior Court Judge Craig L. Parsons postponed the trial out of concern that Oakland shootings could have tainted the jury pool.

Parsons has indicated he intends to tread carefully, since the jury will decide if Alvarez is to die or receive life in prison. He read instructions he was considering to give to the jury that would include a history of the death penalty in California and how the law has changed.

The instructions would have explained why high-profile killers such as Sirhan Sirhan and Charles Manson have life sentences while Alvarez could receive the death penalty.

But Wagstaffe vigorously objected.

"There is not a foundation on earth for that. A history lesson does nothing but confuse (the jury)," he said.

Sirhan's and Manson's death sentences were commuted to life in prison without parole after the U.S. Supreme Court ruled the state's death penalty unconstitutional in 1972. But a new death-penalty law was passed in 1978 through a voter initiative.

Parsons also agreed that jury instructions will include the "Liberman admonition," named after Alvarez's attorney, who raised the issue of restricting use of high-tech devices by jurors during the trial, along with newspapers and news reports.

Jurors will also be restricted from posting on Twitter (called tweeting), blogging or instant messaging or receiving such messages, all of which could cause a mistrial.

The trial resumed Tuesday after a five-month postponement and will continue with jury selection Wednesday. Attorneys' opening statements are expected the week of Oct. 12.

The trial, including the penalty phase, is expected to last until Dec. 16.