WATERLOO - Jurors heard about the mechanics of the human memory as the defense continued its case in the murder trial of Jeffrey Duane Smith on Tuesday.

Smith, 21, is accused of shooting Tonyeah Jackson, 27, to death at Club Crystyles on July 9, 2006.

Four prosecution witnesses earlier took the stand and told jurors they saw the man they knew as "J-Rich," Smith's nickname, open fire at the club. Smith allegedly peeked in through the door, shot Jackson with a 9mm pistol and left.

Otto Maclin, an associate professor of psychology at the University of Northern Iowa, took the stand for the defense Tuesday and told jurors how the brain often fills in the gaps of people's memories when they recall events.

"Our brain is kind of like a morphing program," Maclin testified.

He said it puts together different abstract images to create a single image. Sometimes prior mental snapshots can replace parts of actual memory of an event, he said.

During stressful situations, a person's memory changes focus, he said.

For instance, Maclin said that if he was confronted by a robber with a gun, his mind would be busy evaluating the threat, determining if the robber was armed and seeking possible escape routes. He would less likely be concerned about getting a detailed description of the assailant, he said.

Maclin also talked about how a witness could influence other witnesses' memories by telling them false details.

The defense also continued to delve into its claim that police ignored other suspects in the slaying, including alleged gang members who were found at a home on Woodmayr Drive within minutes after the shooting. Police found a .22-caliber handgun, 9mm ammo and drugs in the house.

One of the men inside, Dontay Sanford, 23, alternately denied any knowledge and asserted his Fifth Amendment rights when posed questions about items found in the house and any connections to Jackson's death.

"I didn't see any drugs," Sanford said. "I didn't see no ammunition."

Defense attorney Robert Montgomery pressed him, asking if the gun that went to the 9mm bullets in the house was the gun used to kill Jackson.

"Plead the fifth," Sanford said.

He then said he had nothing to do with Jackson's death.

When asked if he was a member of the Southside street gang, Sanford first pleaded the fifth and then said "I don't know any Southside street gang."

In other testimony, jurors heard from a jailhouse witness for the defense who countered testimony from a jailhouse witness for the state.

Christopher Houdek, 21, told the jury that Rayshawn McClarity, a witness for the state, told him he was going to make up a story about Smith in order to get a better plea deal from prosecutors in his own case.

"He said 'I'll make it up,'" Houdek said.

McClarity, who had worked with Smith at a supermarket, earlier testified that before the shooting Smith told him he had a 9mm handgun. He also said he later met Smith in the Black Hawk County Jail after the shooting and said Smith told him he shot Jackson because Jackson hit him following an argument with a girlfriend.

Houdek testified that McClarity told him that Smith really denied any part in the shooting. He said McClarity suggested that he, too, make statements to get leniency.