He changed his alibi and gave police detailed descriptions of where his blood would be at the crime scene.

But jurors saw Wednesday that at the end of a nine-hour videotaped statement to detectives, Kansas State University professor Thomas E. Murray walked out of the interrogation room a free man.

“At this point, you don’t have compelling evidence,” Murray told detectives near the end of the video. “If you had compelling evidence, wouldn’t you just go ahead and arrest me?”

Wednesday was the fourth day of Murray’s first-degree murder trial in connection with the November 2003 stabbing and beating of his ex-wife, Carmin D. Ross. It was the second day in a row jurors have spent the entire day looking at a TV monitor showing the interview Murray gave to police in Manhattan the day the body was discovered.

The video, which ended Wednesday, is believed to be a crucial piece of prosecutors’ evidence against Murray. Prosecutors allege he killed Ross in her home northwest of Lawrence in part because he didn’t want to lose custody of the couple’s 4-year-old daughter.

Defense attorneys argue the video shows Murray was willing to help the investigation — a point Murray made to detectives.

“I’m thinking I’m going to be cleared by this,” he said in the video.

But also in the portion of the video shown Wednesday, Murray changed his story about where he was the morning of Ross’ killing.

Initially, he told detectives he dropped off his daughter at a friend’s home in Manhattan, went to his office briefly, and then was home all morning grading papers in his kitchen.

But on Wednesday, shortly after detectives asked him to make a written statement, he said, “One thing occurred to me. I know you’re going to look at this with a raised eyebrow.”

Assistant Dist. Atty. Angela Wilson, from left, talks with Heather Bowman and Samantha Fabbri, during a Wednesday recess in the murder trial of Thomas E. Murray. Bowman and Fabbri are sisters of Carmin D. Ross, Murray's ex-wife who was killed in November 2003.

He told detectives he didn’t stay home all morning, but instead took a drive on Interstate 70 to clear his head and to find pillow covers at an antique shop in Paxico. On the way there, he said, he turned around and came home.

At times, the interrogation took on the tone of a casual chat, such as when Murray asked police about the difference between crime-scene investigation TV shows and real life.

“I’m having fun with it from the ‘C.S.I.’ perspective,” Murray said.

Early Wednesday, jurors heard Murray tell detectives they’d find Ross’ blood in his car because she’d had a nosebleed while borrowing the car days before the killing.

Murray said he’d never think of killing somebody, but if he was capable of murder, it would be by using poison or putting something in the air, not something physical like what he imagined happened to his wife.

He challenged the idea that he could have driven from Manhattan to Lawrence and back in the time in which detectives thought the crime happened.

“I can’t make the numbers work out,” Murray said.

Jury finishes viewing interrogation Day Four Photo Gallery See complete trial coverage

Detective Pat Pollock asked Murray how he would explain it if they found his blood on Ross’ body. Murray said they had stumped him and said he hadn’t bled on Carmin in a long time.

“No, wait,” Murray then said. He told detectives he had blood dripping off his finger when he was at her home that would have gotten on her clothes but not her body.

“That’s the truth,” Murray said. “I’m being as sincere as I can.”

Late in the video, Murray flat-out denied killing Ross. He said he was “a thinking man,” and if he truly had killed Ross he would have come up with all his explanations long ago instead of having to change his story to detectives.

“It occurs to me that in me you have not just a likely suspect but a convenient one,” Murray said. “If this scenario falls apart, you’re very well back to square one.”

Testimony is expected to resume this morning.