In a literal life-sentence-or-death courtroom drama, prosecutors and defense attorneys struggled Monday to determine who shot first in the death of East Palo Alto police Officer Richard May -- despite conflicting testimony of a key witness.

Video and audio-recorded statements by the prosecution's chief witness, Marco Marquez, placed Alberto Alvarez as the initial shooter in the alleged murder of East Palo Alto Police Officer Richard May even as it conflicted with Marquez's courtroom testimony Monday.

Marquez, 19, the police Explorer who accompanied May on a ride-along Jan. 7, 2006, said in separate video and audio recordings that he saw Alvarez fire the first shot at May.

The statements were in stark contrast to the often-emotional witness-stand testimony Marquez gave Oct. 20 in San Mateo County Superior Court, during which he denied seeing either man fire their guns.

The difference in who shot first could determine whether Alvarez faces the death penalty or possible life in prison -- whether Alvarez "executed" May or returned fire from May.

Deputy District Attorney Steve Wagstaffe called five other witnesses Monday, who said they heard the gunshots in an effort to establish a sequence for the six gunshots – five of which were allegedly fired by Alvarez.

The sequence of the shots could prove crucial in whether Alvarez receives the death penalty or a lesser charge. His attorneys have stipulated that he killed May, so that is not at issue in the trial.

May and Marquez pursued Alvarez as a suspect in a reported fist fight at the Villa Taqueria on nearby Cooley Avenue in East Palo Alto. Alvarez allegedly shot the officer multiple times in a resident's driveway on nearby Weeks Street, killing him.

The prosecution claims Alvarez fired at May first, hitting the officer in the shoulder, then firing twice into his bulletproof vest at close range. Alvarez then allegedly stood over the fallen officer and executed him, shooting him in the face as the officer lay stunned on his back.

But defense attorneys said they will prove May exceeded the scope of his duties by striking Alvarez twice with a metal baton in the back, in violation of his department's rules to use the weapon only in self defense.

The defense claims May then shot Alvarez in the leg, prompting the defendant to shoot back. The fatal shot to May in the face was the first shot Alvarez fired, meaning he did not "execute" him after the exchange of shots, attorneys Charles Robinson and Eric Liberman said.

On Monday, East Palo Alto Detective Sgt. Jeff Liu testified that he found Marquez in a room at the back of the East Palo Alto police station at 2415 University Ave. Marquez was alone and crying. He took a few minutes to give the youth a chance to calm down before taking him to the San Mateo County Sheriff's substation on Demeter Street for an interview, he said.

In a video interview two hours after the shooting, a frightened-looking, hunched Marquez told Liu that he and May were driving east on University Avenue in East Palo Alto when they received a dispatch call about a fight at the Villa Taqueria on Cooley Avenue. Previous testimony last week by witnesses established that Alvarez was involved in that fight but did not initiate it.

When the patrol car turned onto Cooley, May and Marquez "saw a man jaywalking" in front of the police car, he said.

May stopped the car and began to get out, but the man took off running north across University Avenue and west to the next block, Weeks Street. May made a U-turn, driving west on University against traffic for a short distance, then turned right onto Weeks Street, where he saw the suspect fumble with his keys to unlock the gate to an apartment complex.

As May stepped out of the car, Alvarez again took off running, Marquez said on the tape.

May pursued Alvarez into a residential driveway at 579 Weeks St., where Marquez said he saw Alvarez pull out a handgun.

"Officer May takes out his baton and tried. ... He strikes at him once or twice. ..." Marquez said.

The suspect was wearing a large, puffy jacket and he did not think the baton had much effect, Marquez said.

"He was in the driveway so he turns around. He put ... first he put his hand inside his, ah, jacket and he turns around and put the gun out and Officer May in ... at that moment he took out his gun ... and they were both firing at each other but I guess the guy shot first. ... And after that he shot Officer May like about seven to eight times ... about six, seven times, I'm not sure," Marquez said.

"Officer May didn't ... got a chance to take out his gun but the guy shot at him ... and Officer May shot once and that other guy was shooting -- the guy was shooting multiple times," Marquez said.

When the shooting started Marquez said he ducked behind the car door and lost sight of the officer. He saw May but after the first shot he didn't see him any more, he said.

He heard more gunfire. After five or six seconds, he saw Alvarez running past him. Alvarez looked at Marquez and kept running with a limp. Alvarez opened the gate and tripped. Marquez saw him fall down. He looked back at Marquez and started running again, the youth said.

Marquez also made an audio recording with San Mateo County investigators Det. Pam Glembot and Sgt. Wes Matsuura at about 9 p.m. that evening at the East Palo Alto police station. Marquez again told the investigators that he witnessed Alvarez draw his gun first, but he added more detail than in his statement to Liu.

Alvarez aimed somewhere toward May's neck, or upper torso, Marquez said.

May and Alvarez were only about five feet apart, Marquez told the investigators.

"It was face to face," he said.

"I heard and I saw the shot ... I, like ... I heard the shot. But then I looked up a little bit. And I saw the, uh, shell casing flew off. So I knew it was him that shot Officer (May) first," he said.

Marquez also said May was still alive when he approached him as he lay in the driveway. May was still breathing but died shortly after another police officer, named Hines, arrived, Marquez said.

Several Weeks Street residents also testified Monday that they heard gunshots.

Shawn Sherrod, who lives next door to the home where the shooting took place, said he heard four to five shots. He peeked through the blinds and saw a man in dark clothing running toward the gate at the apartment building (where Alvarez first tried to gain entry).

He saw the man in profile but was unable to identify Alvarez in court as that man.

Gabriel Ledesma, who lives across the street, said he heard two groupings of gunfire with only a split-second break between them.

Erik Black, who lives at in the residence where the shooting took place, said he had his 1998 Dodge Dakota truck thoroughly cleaned earlier that week but had not driven it out of the driveway since it was washed. Prosecutors said during opening statements that police found Alvarez's handprint on the truck.

Black said he and his girlfriend heard four or five shots. As he looked out the living room window, "I saw some legs hanging out from behind (an) Oldsmobile" stored in the driveway.

Patricia D'Larzelera, whose home is opposite the site of the shooting, said she heard gunshots "in two bunches" -- three shots with a slight pause and then three more.

When she looked out her front door she saw a police car (May's) with the driver's side door open "but no policeman in it."

"I thought 'Uh-oh. No good," she said.