COLUMBIA, ILL. — The police department here has bought additional surveillance cameras after the murders three months ago of Sheri Coleman and her two sons, but they say it's not an expansion of the city's surveillance network.

The Columbia police paid $4,389 last month for an expense labeled as "surveillance cameras for investigation," according to the city's payment documents. The expense was included with credit card payments for other equipment purchased for the Major Case Squad's investigation into the slayings.

Police Chief Joe Edwards said the cameras were not additions to the city's existing network of about 10 cameras, which are monitored in real time by police. He wouldn't disclose what role the new cameras played.

"I will not discuss anything related to the Major Case Squad investigation," Edwards said in an e-mail to the Post-Dispatch.

Christopher Coleman, 32, is charged with three counts of first-degree murder in the strangulation of his wife Sheri, 31, and sons Garett, 11, and Gavin, 9, whose bodies were found in their home May 5.

Police said Christopher Coleman was having an affair with Tara Lintz, a high school friend of his wife from Florida. Expense documents show travel vouchers for detectives' trips to Florida.

Long before the killings, the city had surveillance cameras trained throughout the town, some in residential neighborhoods.

One camera is posted near the city's water tower at the entrance to the subdivision where the Coleman family lived. It remains unclear what role, if any, it played in the investigation.

A Columbia police officer, who lived near the Colemans, had a home surveillance camera that was able to show Coleman left his home at 5:43 a.m. on the morning of the murders. Coleman told police he had gone to a gym that morning.

According to expense documents, police also bought a $411.84 mobile DVR and $590.05 for computer hard drives for the investigation.

In April, the department spent $4,588.93 on new surveillance monitors. Dispatchers monitor them from a control room at the police station.

Earlier this year, the American Civil Liberties Union had criticized Columbia's surveillance network, saying the city had spent in excess of $50,000 on surveillance cameras without disclosures about their use.

Columbia officials have said they have no policies or guidelines restricting the use of the cameras.

"The department employees who have access to the camera system are required to log in with a user name and password and everything that is done is recorded," Edwards said.