(CNN) -- The pastor of a Maryville, Illinois, church was shot to death during a service Sunday in front of horrified church members who then tackled the gunman, state police said.

The Web site for the First Baptist Church of Maryville, Illinois, includes a photo of the Rev. Fred Winters.

Fred Winters, the pastor of the First Baptist Church, was shot and killed during the 8 a.m. service, and the attacker and two church members suffered knife wounds in the attack, authorities said.

The gunman entered during the service and walked up to the pulpit.

Winters and the gunman apparently exchanged words before the 27-year-old man fired four shots, hitting the pastor's Bible and then the pastor, said Illinois State Police Director Larry Trent.

"The only thing we know is that the suspect said something to the pastor, and the pastor said something back to him -- we don't know what that was," Trent told reporters Sunday afternoon. "It was almost as if the pastor may have recognized him, but we're not sure about that at all."

The gunman's .45-caliber pistol jammed after he shot Winters, Trent said. The man then pulled out a knife before being tackled by some of about 150 worshippers attending the service in southern Illinois, near St. Louis, Missouri. Watch the aftermath of the church shooting »

Earlier reports from authorities said the man may have turned the knife on himself, but Trent said that was not confirmed.

"When he was tackled by two of the members, we don't know whether he fell on the knife, injuring himself at the time, or whether [his injury] was self-inflicted during the struggle," Trent said.

Two of those who went after the attacker suffered injuries that aren't life-threatening, while the suspect's injuries are "very serious," Illinois state police spokesman Ralph Timmins said.

Witness Claudia Bohley told CNN affiliate KSDK-TV in St. Louis that she was in the church's foyer waiting for the service to begin when she heard "pop, pop, pop. ... We just couldn't imagine what had happened."

She said she ran into the sanctuary and saw what looked like paper scattered on the pulpit. She said she was later told that a bullet hit Winters' Bible.

"It was like confetti. It went everywhere," she said. "People were down on their knees and on the floor, screaming and praying."

She described Winters -- who is pictured on the church's Web site along with his wife and two children -- as "such a pleasant pastor."

Trent said police are still trying to determine a motive in the shooting and that church members did not recognize the gunman.

St. Louis University Hospital spokeswoman Laura Keller told CNN three males, including the suspect, were brought to the hospital. One was dead on arrival, she said, but the hospital was not releasing names and ages. She said the second was in an operating room and the third was the suspect, whose condition was not immediately available.

Trent said one of two wounded church members was treated and released.

Trent called the actions of the two wounded church members "heroic," saying they took quick action when others "were understandably stuck to their seats."

Phone calls to the church office went unanswered Sunday. A posting on the church's Web site said a prayer vigil would be held at 6 p.m. at Metro Community Church in Edwardsville, Illinois, about six miles north of Maryville.

First Baptist Church is fairly large, with about 1,000 members, KSDK reported. The church holds four Sunday services.

Timmins said many of the people attending the service remained for hours afterward, as police were conducting interviews.

The Illinois shooting is believed to be the nation's first in a church since July, when a 58-year-old man opened fire in a Knoxville, Tennessee, church during a children's play. Two people were killed and six wounded in that shooting at Tennessee Valley Unitarian Universalist Church.

In the Tennessee case, Jim Adkisson told police he targeted the church because of its "liberal teachings," according to court papers. Adkisson pleaded guilty last month in a deal that allowed him to avoid the death penalty and will face life in prison without parole, court officials said.

Police said the Maryville congregation had a plan in place, including a protocol for lockdown, in the event of an incident such as Sunday's attack.

All About Shootings • Illinois