POPLAR BLUFF, Mo. -- Law enforcement officers maintained a presence at Poplar Bluff schools Tuesday after bomb threats were called in earlier in the morning to the schools and the Butler County Courthouse.

The schools were on lockdown for more than two hours as officers conducted security sweeps at each building.

"All the security sweeps didn't reveal any viable threat," according to Poplar Bluff Deputy Chief Jeff Rolland. "Officers will maintain a heightened presence at all the campuses throughout the day."

The schools went on lockdown after a total of three bomb threats were made.

"The first threat went to the [Butler County] courthouse at about 10 [minutes] after 8 [p.m.]," indicating there were bombs at the courthouse and the schools, Rolland said.

About 15 to 20 minutes later, Rolland said, there were "two calls at another location, and that call specifically mentioned the courthouse and the high school."

After the alleged threats were made, authorities secured the schools, put them on lockdown and began security sweeps, Police Chief Danny Whiteley said.

The courthouse was evacuated in about five to 10 minutes, Butler County Sheriff Mark Dobbs said.

"We were careful as to how we evacuated it so no more people than had to were standing in the parking lot," Dobbs said. "Some of the employees and officeholders were evacuated through the tunnel [under Pine Street] to the sheriff's department."

Once everyone was evacuated, Dobbs said, a search was conducted by officers with the sheriff's department and police department, as well as by members of the Butler County Emergency Management Agency.

He said everyone was allowed to return after about 30 minutes.

"It was just a general threat; there was no specific area given," as to where a bomb may have been placed in the courthouse, said Dobbs, who described it as being "generally a pretty secure operation, especially at night."

As operations were resuming in the courthouse, members of the police and sheriff's department, as well as the Missouri State Highway Patrol, were in the process of doing security sweeps at the schools, Rolland said.

Both the Poplar Bluff Fire Department and Butler County Fire Department had been "made aware and are on stand by, as is the SEMO Bomb team" as the sweeps were done, Rolland said.

"We are keeping law enforcement officials at the schools for precautionary measures, [and] we are actively pursing leads to bring the individual responsible to justice," Rolland said.

According to Rolland, officers also are investigating whether a bomb threat made between 10 and 11 a.m. Sunday at the Wal-Mart Supercenter may be connected.

"We're not ruling anything out [and are waiting for] the investigation to progress to tell us it its connected," Rolland said.

The store was not evacuated, but a security sweep was done and additional security were posted, Rolland said.