(CNN) -- The stepfather of a missing Maryland boy was charged Thursday with first-degree murder after the boy's mother was found dead, police said.
Curtis Lopez, 45, was arrested Thursday morning in Charlotte, North Carolina, after a warrant was issued, said Chief Tom Manger of the Montgomery County, Maryland, police.
An Amber Alert has been issued for the boy, 11-year-old William McQuain, who remains missing, police said.
Homicide detectives from Montgomery County were on their way to Charlotte on Thursday.
"Our focus and our priority now is locating William McQuain," Manger told reporters Thursday. He held up two pictures of the sixth-grader, one a class picture and the other showing him in a baseball uniform.
The case began Wednesday afternoon when a friend of the boy's mother reported her missing, saying he had not seen her for about two weeks and that he was concerned for her welfare, Manger said. Police learned her son had not been in school since Sept. 30.
When detectives arrived at the woman's home in Germantown, they found Jane McQuain, 51, dead in her bedroom with evidence of trauma to her upper body, Manger said. Her son was not there and the woman's vehicle, a Honda CRV, was gone.
Lopez was McQuain's husband and had been known to frequent her residence but did not appear to live there, Manger said. Witnesses told police they saw him recently at the home, removing property and loading it into McQuain's Honda, he said.
The car was found Thursday morning, but police would not reveal where.
Detectives contacted Lopez on Wednesday night, before they found McQuain's body, Manger said. Once the body was found and the case was ruled a homicide, Lopez, based on his inconsistent statements, became a person of interest, he said.
"We were hoping that we would find (William) with Mr. Lopez and we did not, so we are asking for the public's help in locating 11-year-old William McQuain," Manger said.
"My hope is that he may be with a family member or a friend that perhaps has no idea what's occurred with his mother, but as time goes on it becomes, I guess, more and more of a long shot that that's the case," he said.
Jane McQuain was probably dead for 10 to 12 days before police found her, Manger said.
Police believe Lopez may have had a residence in North Carolina, Capt. Paul Starks of the Montgomery County police told CNN, but they have few other details linking him to the area.
William McQuain is described as a light-skinned African-American, about 5 feet tall and weighing about 85 pounds.
Anyone with information on his whereabouts is urged to call 911, police said.
CNN's Brittany Kaplan contributed to this report.