While pro-life supporters marched in Washington, D.C., on the anniversary of Roe v. Wade, Friday, an abortion-related trial began in Kansas.

Scott Roeder confessed to killing Dr. George Tiller who was one of the few late term abortion providers in the country.

As Roeder's murder trial gets underway on the 37th anniversary of the ruling that legalized abortion, activists on both sides of the issue focused in.

The prosecution began by playing 911 calls from witnesses.

Click play to watch Mark Martin's report followed by insight from Wendy Wright of Concerned Women for America.

Police say Roeder walked into a Kansas church last May, and shot Tiller at point blank range and threatened two others.

"I saw out of my right vision. I saw a flash and I heard a pop, to me sounded like a balloon popping," witness Kathy Wegner recalled. "Then I just saw Dr. Tiller just fall flat on his back. I just saw him flat on his back and I thought, 'why is he there?'"

"And when I saw the flash and heard the gun pop I looked because it was just right there and I saw an assailant with his hand out and he still had the gun in his hand," she continued.

During his career, Tiller defended his work as a late term abortion provider.

"I have a right to go to work," he once said. "What I do is legal. What I do is ethical and you're not going to run me out of town."

Tiller's clinic closed after his death.

Roeder's defense team will argue that taking Tiller's life was necessary to protect unborn children. Tthe trial could involve hundreds of witnesses, including Roeder's ex-wife and son.

*Originally published January 22, 2010.