A relative with a lengthy criminal history has been arrested in the fatal shootings of a mother and son inside their Fort Washington home earlier this month, police said.

Quindell G. Mercer, 34, is charged with two counts each of first- and second-degree murder in the Aug. 4 slayings of Patricia Harris, 56, and son, 20-year-old Frank L. Harris, court records show. Mercer was Patricia Harris’s son and Frank Harris’s half-brother, law enforcement sources have said.

Quindell Mercer (Courtesy Prince George's County Police Department)

Mercer had been unaccounted for since Patricia and Frank L. Harris were found shot to death early one morning on the main level of their home in the 11800 block of Hickory Drive. Police were called to the scene by Patricia’s husband and Frank’s father, who discovered their bodies, authorities have said.

There were no signs of forced entry at the home, and immediately, scrutiny turned to those who knew the Harrises and would have had access. About a week later, Prince George’s police said publicly that they were searching for Mercer as a “person of interest” in the case.

Court records show Mercer, who has no fixed address, has had extensive contacts with police in the past, including convictions in Prince George’s for first-degree assault and carrying a handgun. He was also wanted on assault warrants in North Carolina, authorities said.