EL CAJON, Calif. -- A deadlocked jury prompted a judge to declare a mistrial Monday in the case of a man charged with murder in connection with a robbery that ended in the shooting deaths of two El Cajon liquor store clerks.

Anthony James Miller, who is accused in the March 1, 2006, killings of Heather Mattia and Firas Eiso, testified that co-defendant Jean Pierre Rices ordered him to participate in the crimes.

Jurors deliberated over parts of four days before telling El Cajon Judge Lantz Lewis they were deadlocked 11-1 for guilt.

The judge scheduled a retrial for Sept. 28, said Deputy District Attorney Jennifer Kaplan. The defendant faces life in prison without the possibility of parole if convicted.

Miller testified that he was 20 years old when Granada Liquor was robbed, and Mattia -- the sister of the store's owner -- and Eiso were slain.

Miller said he, Rices and Nichelle Delon Hopson were driving around looking for something to do when Rices told Hopson to pull over at the store so they could get some drinks.

The men got out of the car and Miller said he saw Rices pull a handgun from his waistband. It was the first time he had seen the weapon that night, he testified.

Rices then tossed him a bag and told him what he was supposed to do, Miller said.

"It was in a demanding tone, like 'you're going to take some of this money for me,'" Miller said. "I was actually scared out of my wits. I didn't know what to do."

Miller, now 23, said he'd never been in a robbery before but wasn't about to challenge Rices, who was armed and had a reputation for violence.

"I really didn't think I had a choice," Miller testified.

He said when he went into the store, Mattia, 22, and Eiso, 23, were on the floor.

Rices ordered him to check the cash registers for money, but he couldn't find any, Miller testified.

The witness said Mattia actually told him where money was located. When he put about $1,250 in the bag, Rices ordered him to leave and have Hopson start the car, he said.

Rices joined them moments later. Miller testified that he did not hear the gunshots that killed the clerks, but was aware that Hopson testified that she did hear them.

Both victims were killed by a single gunshot to the back of the head.

In addition to Miller's trial, a separate jury is hearing the penalty phase of trial in the case against Rices.

Rices, 27, has already pleaded guilty in the case. His jury will decide whether to recommend the death penalty or life in prison without parole.

Hopson, 24, who was Rices' girlfriend at the time, pleaded guilty to voluntary manslaughter in exchange for her testimony.

Rices was arrested several months after the liquor stores murders when a die pack exploded after a bank robbery in Lakeside.

Miller said detectives didn't come to him until November 2006, and he conceded that he initially lied to them in hopes he wouldn't get in trouble.

His attorney, Daniel Mangarin, told jurors in his opening statement that his client was not a strong enough person to face up to Rices, who was released from a five-year prison stint only a few months before the murders.

Prosecutor Glenn McAllister said participating in the crime makes Miller liable for the deaths.