WASHINGTON (CBSDC) - A man in the District was sentenced Thursday for the armed robbery of his elderly grandparents after they gave him a job and place to live.

Riley Mercer, 40, was sentenced to 22 years in prison for the masked armed robbery he committed on his grandparents with the help of two others.

He was found guilty in June, after being brought up on charges of conspiracy, burglary while armed, kidnapping while armed, armed robbery of a senior citizen and related weapons offenses.

The trial revealed that Mercer had come to live with his grandparents, who are in their 70’s, at their home in Northwest in 2010. They gave him a key to their home and a job with their security company.

During his employment he learned his grandparents kept cash for their employees’ payroll in a safe in their bedroom closet and that his grandmother was the only person with the combination.

In the early morning hours of Sept. 29, 2011, Mercer and two others, who have remained unidentified, entered the home wearing masks, went directly into his grandparents’ room and pointed guns at the elderly victims.

One of the men walked over to Mercer’s grandmother and led her to the closet where the safe was kept. When he threatened to shoot her for moving too slowly, she overheard Mercer’s voice say the words, “Don’t hurt her.”

She was certain it was the voice of her grandson.

The men fled after retrieving close to $15,000 in cash, leaving Mercer’s grandparents tied and bound on their bed. The eldest daughter eventually heard their cries for help and rushed in to untie them.

At Mercer’s sentencing, the judge presiding over the proceedings noted the horrific nature of the crime and how frightening the ordeal must have been for the victims.