San Diego- A South Bay man consumed with thoughts of torture, murdered and butchered a transient friend, then dumped his body parts all over San Diego County, a prosecutor said Thursday.

Authorities don’t know why Gerald Nash [pictured] killed Allen Hawes — cutting off his head, hands and legs — but speculated that it could have been because of a dispute, or the defendant was trying to create a new identity, or because Nash enjoyed it, prosecutor Kristen Spieler said in her opening statement of trial.

Defense attorney Troy Britt told the jury there was no direct evidence that Nash shot the 57-year-old victim in the head, then used a saw to cut off his body parts and scatter them throughout the county.

“Nobody’s going to come up and say, `I saw that happen,”‘ Britt said in his opening statement. “You’re not going to get that kind of evidence.”

But Spieler told the jury that Nash, 62, appeared nervous when police questioned him about Hawes, who was known to stop by the Egger Highlands adult video store where the defendant worked the graveyard shift.

Hawes — known by some as “Backpack Al” because he always carried a backpack — stopped coming by the Ever So Naughty store when Nash quit in December 2006, Spieler said.

The victim’s torso was found about a mile from the store on Feb. 26, 2007, in the Otay River bed, in Palm City.

Hawes’ head was found inside a bag the next morning along Interstate 5 and 28th Street, the prosecutor said.

Within an hour of that discovery, a Caltrans worker found a human hand near southbound 163 and the Interstate 5 split, Spieler said.

Nash was arrested on March 1, 2007.

Five weeks later, in April 2007, two very badly decomposed legs were found in Harbison Canyon in East County, the prosecutor said.

When detectives went to Nash’s home — located behind the adult store — they searched the trunk of one of his three cars and found a blade from a saw and red duct tape similar to tape found near the torso, Spieler said.

Another of Nash’s cars had trash bags covering the seats, and a van belonging to the defendant had a bleach bottle and a reddish/brown stain similar to blood nearby, the prosecutor said.

Police found the victim’s backpack in Nash’s storage unit when the defendant took them there, Spieler told the jury.

Nash told police he last went to the unit in early February, and records show he had been there Feb. 22, 2007, the prosecutor said.

Nash disappeared Feb. 28, 2007, after being questioned about his friend’s disappearance, Spieler said.

The defendant’s roommate told a detective that he saw Nash take a bag of trash out to the dumpster before he left.

In the dumpster next to Nash’s residence, detectives found 40 pages of handwritten notes referencing murder and dismemberment, the prosecutor said.

Words like “disposal, cutting time, wash the saw, drop site, and test ropes,” appeared in the notes, Spieler told jurors.

“With this I could retire,” one of the notes read.

“Get the wallet above all,” read another.

Police also found plastic drink bottles that had been modified to be used as home-made silencers, the prosecutor said.

Pieces of wet carpeting with red/brownish stains that looked like blood with a strong smell of bleach were also found in the dumpster, Spieler said.

After Nash was arrested, police found three weapons — including a .357 revolver with ammunition — in the trunk of car he had bought after police initially questioned him, the prosecutor said.

Fragments from a test-fire on the gun matched bullet fragments taken from the victim’s brain, Spieler said.

The victim’s blood was found in Nash’s van and on gloves in the dumpster, and Hawes’ DNA was discovered in a hole on the saw blade, even though the blade itself had been wiped clean, the prosecutor said.

Spieler said a middle fingernail was missing from one of the victim’s hands and investigators from the Medical Examiner’s Office claimed it couldn’t have been an accident.

The prosecutor said Nash had notes on methods of disposing a body, including burning and leaving it for wild animals.

But Britt countered there would be no evidence presented that Nash dismembered his friend and that doing so “would be a messy chore.”

The attorney said no witnesses will testify that they saw Nash driving around San Diego County throwing body parts out the window of his car.

He said all of the body parts were found in heavily traveled areas except for the legs.

Nash had no motive to kill Hawes, Britt said. He said the defendant gave the victim money and a place to stay.

“They were friends,” Britt said. “Mr. Nash was helping Mr. Hawes and helped him for seven years. Mr. Nash went out of his way to help his friend.”

The attorney said there wouldn’t be enough evidence to prove Nash chopped up his friend and threw him out in the garbage like a “piece of human refuse,” a “piece of trash.”

Nash — who is charged with murder and personally discharging a firearm – -faces 50 years to life in prison if convicted.