The needle of a car’s gasoline gauge was the central point of testimony Monday in the trial of a Kansas State University professor charged with murdering his ex-wife.

Using testimony from a detective who retraced professor Thomas E. Murray’s driving routes, prosecutors tried to show there was a quarter-tank of gasoline unaccounted for in the tank of Murray’s Saturn sedan. They say that amount would have enabled him to drive from Manhattan to Lawrence, stab and beat Carmin D. Ross, and drive back.

But defense attorneys say the experiment proves nothing, given that no one knows whether Murray started with a full tank.

Monday was the beginning of the fourth week of Murray’s murder trial, and prosecutors are expected to finish presenting their case by Wednesday. Murray is charged in the Nov. 13, 2003, stabbing and beating of Ross at her home northwest of Lawrence at 1860 East 1150 Road.

Law enforcement officers know Murray bought 9.5 gallons of gasoline on Nov. 11, 2003, Douglas County Sheriff’s Detective Lyle Hagenbuch testified on Monday.

When they examined his car Nov. 14, Murray had a quarter-tank left. He told detectives every place he’d been during those three days, including a Chinese restaurant, his office, the baby sitter’s and a drive along Interstate 70 to “clear his head.” He said he had not been to Lawrence.

So Hagenbuch and another detective got a car similar to Murray’s, filled it up at the same gas station where he bought gasoline and drove everywhere he said he’d been.

Douglas County District judge Robert Fairchild, seated center, is questioned by, from left, prosecutor Tom Bath and defense attorneys Robert Eye and Pedro Irigonegaray on Monday during the murder trial of Thomas E. Murray.

When they finished, the car’s tank was half-full.

The next day, detectives did the same experiment, with one addition. They drove from Murray’s home in Manhattan to Ross’ home and back.

When they finished, the tank was one-quarter full.

Defense attorney Bob Eye asked Hagenbuch how much gasoline was in Murray’s tank before he added gas on Nov. 11. Hagenbuch said he didn’t know.

Eye asked Hagenbuch how many times Murray had put gasoline in his car after Nov. 11. Hagenbuch said he didn’t know.

Also on Monday, Sheriff’s Detective Pat Pollock again took the witness stand to testify that officers tried to interview Murray after his initial statement, but he wouldn’t talk with them.

6News video: Murray investigators raise questions of missing gas Day Twelve See complete trial coverage

“On advice of counsel, he was no longer available to be re-interviewed,” Pollock testified.

On cross-examination, defense attorney Pedro Irigonegaray asked, “You don’t see anything wrong … with a citizen retaining counsel when he or she is being made the suspect on a first degree murder case based on suspicion, a hunch, an intuition, do you?”

“No, I don’t,” Pollock answered.