Slain Texas District Attorney Mike McLelland, wife to be honored at public memorial

Updated at 9:41 a.m. ET

MESQUITE, Texas Gov. Rick Perry and law enforcement officers from as far away as Britain are expected to attend a public memorial for a slain Texas prosecutor and his wife.

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CBS News correspondent Anna Werner reports from Kaufman, Texas, that Perry is expected to join a group of elected and law-enforcement officials later Thursday to announce a six-figure reward for any information leading to an arrest in the murders of Kaufman County District Attorney Mike McLelland and his wife, Cynthia.

"We're also going to do everything that we can to track these individuals down and to dispense appropriate justice," Perry told CBS News Wednesday.

Officials are hoping that a bigger reward fund will bring in some much-needed tips on the case, Werner reports.

Officials with The Honor Network say an overflow crowd is expected Thursday in a suburban Dallas church for the ceremony to honor the McLellands. Both were found shot to death Saturday in their house near Forney, about 20 miles east of Dallas.

No arrests have been made.

The public memorial will be at 1 p.m. Thursday at First Baptist Church of Sunnyvale in Mesquite. The funeral will be 10 a.m. Friday at First Baptist Church in Wortham. Burial will be at Wortham Cemetery.

Wortham, where McLelland grew up, is 75 miles south of Dallas.

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Neighbors of the McLellands have told CBS that a beaten-up, white SUV was parked at a corner near their house for four days before Saturday's shooting and that there appeared to be four men inside.

Police are looking at tire tracks and cigarette butts found near their home.

McLelland is the second prosecutor from that district to be killed since January.

CBS News senior correspondent John Miller, a former deputy director of the FBI, reports that the shootings are having an effect on Texas law enforcement.

McLelland's replacement in Kaufman County, interim District Attorney Brandi Fernandez, is working in what Miller described as "an armed camp" at the courthouse with a 24-hour protective detail.

Sheriffs in other Texas counties, including those surrounding Kaufman, told Miller that they are also putting their district attorneys under 24-hour protection.

Also, an assistant U.S. attorney handling a major criminal case against the Aryan Brotherhood of Texas, which has been mentioned as possible suspects of the killings in Kaufman County, recused himself, citing safety concerns.

"That never happens," Miller told "CBS Evening News" anchor Scott Pelley. "That shows a crack where law enforcement is showing signs of being intimidated, and that's something they never want to show to the public."