OAKLAND -- The simplest explanation for a series of events usually reveals the truth, a prosecutor said Monday as he urged a jury to find an ex-felon guilty of murder in a case based largely on circumstantial evidence.

Deputy District Attorney Greg Dolge told jurors that the only just verdict in the case is a first-degree murder conviction -- despite a lack of eyewitnesses or physical evidence directly linking Gregory Gadlin to the killing.

"The answer in this case isn't rocket science," Dolge said. "The evidence is clear and pointing all in one direction, and that is right at the defendant."

Gadlin, 45, is accused of killing Evan Meisner, 22, during a marijuana deal that occurred just after midnight on March 31, 2011, in a house Meisner was renting on Lyon Avenue in East Oakland.

Meisner, who was not a drug dealer, had recently been given a quarter pound of marijuana as payment for helping a friend earlier that month. Needing money to pay rent, Meisner told friends he was going to sell the marijuana to a neighbor.

On the evening before he was killed, Meisner told a friend at dinner that he planned to make the sale later that night to a "big black man" who was a neighbor and who had recently been released from prison.

Meisner said he would return after the sale, even leaving a half-empty beer in his friend's fridge to finish upon his return. Meisner, however, never came back and was found by his landlord later that morning, laying face down with his head in a pool of blood.

Police concluded from the evidence at the scene that Meisner was robbed and that he was probably shot while either on his knees or crouched down on his hands and knees. Meisner's personal belongings were gone, and his pants appeared to have been pushed down as if someone had rifled through the pockets, Dolge said.

Meisner had one bullet wound to the side of his face.

The case was a mystery until police learned Meisner's cell phone number and retrieved records that showed a series of phone calls between him and another number later linked to a cell phone that was owned by Gadlin's wife but used by Gadlin.

A couple of days after the killing, Gadlin, who was on parole after serving prison time for robbery, was arrested on a domestic abuse complaint. While in jail, a phone call he made to a friend was recorded. During that conversation Gadlin asked the friend to retrieve something from the trunk of Gadlin's car.

"This is very important," Gadlin is heard saying on the recording. "Under the big box ... just pick the big box up and you'll see. I need you to do that tonight. It's imperative."

Police, however, got to the car before Gadlin's friend. Under the box investigators found the weapon used in the slaying, a 9 mm semi-automatic handgun.

Further investigation uncovered a Gadlin family member who testified that she bought about a quarter pound of marijuana from the felon a day after the killing.

"He killed Evan to eliminate a witness, the only witness -- that is what's going on here," Dolge said as Gadlin smirked, shaking his head. "Usually, the simplest explanation of the evidence is the correct one."

But Gadlin's attorney, assistant public defender William Keep, said the explanation is not simple and urged the jury to remember that the prosecutor must prove the case beyond a reasonable doubt.

Keep said no evidence was presented proving Gadlin was in possession of the cell phone Meisner called before the killing and said there was no evidence showing that the gun was not planted in the car by someone else before the police retrieved it.

As for his client's recorded jail house call, Keep said Gadlin was just making sure his trunk was clear of anything that could get him in trouble for violating parole.

"He's on parole and he feels that somebody has put something in the trunk of that car to get him in trouble," Keep said. "He didn't put any gun in there."

The jury began deliberating the case Monday afternoon.