St. Louis County Police said they captured a prisoner on Thursday evening, hours after he walked out of a hospital in south St. Louis County and set off a large search involving local, state and federal officials.

Tommy Wayne Boyd was arrested in the 7300 block of Watson Road in south county. Police said they found him after following up on tips from members of the public.

Boyd had been taken from the Potosi Correctional Facility to Mercy South Hospital for medical care. He is serving a 30-year sentence for statutory sodomy. According to police, hospital staff last saw him at 3:54 a.m. Thursday, and surveillance video shows him leaving the building.

Lt. Col. Jason Law of the St. Louis County Police described Boyd as dangerous while the search was still under way. "This suspect is a dangerous person. But we brought in the resources needed so that if anybody sees this suspect, call 911," Law said. He urged residents to report any sighting but "not approach this suspect."

Joe Poelker, a spokesman for Mercy, said in an email that two Department of Corrections officers were with Boyd when he arrived at the hospital. He said there was no physical confrontation and no one was hurt. Police searched the campus, Poelker said, and the hospital's security team checked all buildings and found no sign that Boyd was still inside. He said Mercy was continuing to help police with the search and investigation.

Law deferred to the Department of Corrections when asked how Boyd was able to leave. A spokeswoman for the department said the agency is investigating how the escape happened.

The Mehlville School District placed Hagemann Elementary School, Trautwein Elementary School and Washington Middle School on lockdown during the search. All students and staff were brought inside and exterior doors were locked. The district said classes were able to continue without interruption inside the buildings. Later in the afternoon, it cancelled all after-school activities at its elementary and middle schools.

Asked what parents of students at those schools should do, Law advised them to go about their normal day. "If you see someone who looks suspicious, call 911, and we'll be there immediately," he said.