An American couple living in Uganda accused of torturing their 10-year-old foster child could face the death penalty if convicted of their latest charge, prosecutors said.

Nicholas Spencer and Mackenzie Leigh Mathias Spencer, both 32, were arrested and charged earlier this month with aggravated torture, which carries a life sentence if convicted, for alleged abuse spanning two years.

This week, they were also charged with aggravated child trafficking, which carries the death sentence if convicted, Joan Keko, an attorney with the Ugandan state prosecutor's office, confirmed to ABC News.

The Spencers previously pleaded not guilty to the aggravated torture charge, The Associated Press reported. They will be able to plead to the new charge once the case moves to a higher court, according to the AP.

The two are being detained at a maximum-security prison in Luzira, a suburb of the capital of Kampala, and were not granted bail after being determined a flight risk, Keko said.

The couple allegedly "constantly tortured" the foster child between 2020 and 2022, which "attracted the attention of neighbours," who notified Kampala Metropolitan police, according to a statement from the Uganda Police Force.

The child was allegedly locked in an empty room, without clothes, food or water, and a medical report showed beating marks on his body, according to Kampala Metropolitan spokesperson Luke Owoyesigire.

Police received video evidence from a neighbor and nurse who were checking on the child, a Kampala police source told ABC News.

he Spencers are originally from South Carolina, according to Keko. They moved to Uganda in 2017 as volunteers, police said.

The couple fostered three children in 2018, including the one they were alleged to have tortured, from an organization called Welcome Ministry, in Jinja City, police said. The couple then joined a private company and moved to Upper Naguru, a neighborhood in Kampala, police said.

Their work permit expired in 2021, according to Keko.