Last Updated May 21, 2015 4:25 PM EDT
CLINTON, Mo. -- A Missouri woman who authorities said had been held captive in a wooden box for months before being freed about three weeks ago has been found dead, along with her 17-year-old son.
Clinton police say 46-year-old Sandra Kay Sutton and her son, Zachary Wade Sutton, were found dead early Thursday of what appeared to be gunshot wounds.
Lt. Sonny Lynch says Sedalia authorities are searching for Sutton's former boyfriend, 47-year-old James Barton Horn, Jr. Horn was charged earlier this month with kidnapping, armed criminal action and unlawful use of a weapon for allegedly keeping Sandra Sutton in a box for four months, and has been on the run since.
Lynch called Horn "absolutely" a suspect in the deaths.
Police said Sandra Sutton's car was found after the murder Thursday by a patrol officer at a hospital in the area of Horn's Sedalia home. Surveillance video captured a person they believe is Horn leaving the car and heading in the direction of several abandoned homes.
Sedalia police have blocked off the area and believe he may be in one of the homes. The possible standoff was still developing Thursday afternoon.
Police were initially alerted to the case last month after a "hysterical" woman fled Horn's Sedalia residence April 30. The frantic woman called 911 from a neighbor's home to say she had just managed to escape.
"When officers contacted the victim, she told them the suspect routinely locked her in a wooden box inside the residence where they lived," according to a Sedalia Police Department news release. "Upon responding to her residence, officers did observe a large wooden box consistent with what the female described."
The box appeared "to be constructed for the purpose of concealing a person," police said.
The Sedalia Democrat reported that Sutton said she had been held captive since January after her consensual relationship with Horn turned sinister.
Sutton told police that Horn had threatened her in a car with a "tire jack" after an argument in January. When they returned home, he began building a wooden structure, and she had to help with its construction, according to a probable cause statement filed by Sedalia police.
Sutton was allowed to leave the box in the evenings when Barton returned home from work, according to court documents.
Police said the box was kept in a bedroom and contained a bucket full of urine and feces. The box, which investigators said was 100 inches long, 48 inches wide and 52 inches tall, also contained several layers of insulation, padding and sleeping bags, and a small air hole.
Sutton and her son were found dead early Thursday at a home in Clinton -- about 45 miles southwest of Sedalia -- where Sutton had been staying with relatives, reports CBS affiliate KMOV. Lynch said she had moved away from Sedalia, where Horn had held her captive.
Her son was reportedly a junior at Clinton High School.
Court documents show that Horn has a history of torturing and holding captive women who are breaking up with him, CBS affiliate KCTV reported earlier this month.
Federal prosecutors in North Carolina said that Horn was a sexual sadist who should be institutionalized after he finished a prison sentence, but a judge found that Horn had changed his ways and ordered his release, reported KMOV.
Horn served about three years in prison in Tennessee in the early 1990s in connection with a kidnapping and sexual attack. Records also show that he pleaded guilty in 1997 in Mississippi to unlawfully kidnapping and abducting his estranged wife. He was sentenced in that case to 12 years and 11 months in prison, plus five years' supervised release.
He was released from custody in December 2011, and his probation jurisdiction was transferred in 2012 to Missouri, according to online court records. It was unclear Thursday if he was still under federal supervision.
Messages left for the federal probation office in Jefferson City, which was handling his case, weren't immediately returned. His attorney in that case declined comment Friday.
Sandra Sutton was initially placed in protective custody after her escape from captivity, reports the station.
Lynch said Clinton authorities weren't aware that Sutton had moved to the area.
"As far as I can tell from checking, she has never even sought an order of protection against James Horn," Lynch said. He said authorities are "still investigating those types of issues."
The Pettis County prosecutor's office did not immediately return messages seeking information about the case.