When Theodore Reginald Spencer — “Reggie” to his friends — was questioned by homicide detectives in the killing of 61-year-old Glenn Scarborough, it didn’t take long for him to confess, according to D.C. police.

As for the gruesome particulars of the killing, police said, Spencer, 21, had a simple explanation: “Reggie said he wanted to make sure Glenn was dead so he wouldn’t tell the police who did it,” a detective wrote in a D.C. Superior Court affidavit.

Police found Scarborough, who lived in the Trinidad neighborhood of Northeast Washington, dead June 19 on the floor of his basement apartment.

He had been bound, stabbed, beaten and kicked, authorities said. A wad of paper towel had been stuffed in his mouth, his head had been duct-taped and he had been strangled with a belt.

Spencer’s mother had been dating Scarborough, detectives said. They said Spencer, while being questioned after the killing, told them about a night in June when he had visited his mother, a cancer patient, in a hospital.

“He said he overheard doctors say that his mother had been sexually assaulted, which resulted in her contracting [a sexually transmitted disease],” the affidavit says. “Reggie assumed Glenn was responsible and became angry and left the hospital.”

Police allege that Spencer, of Unionville, Va., about 80 miles south of Washington, recruited two acquaintances to help him take revenge. The two men, Terrell A. Wilson and Phillip C. Swan, both 19, lived near Spencer.

The three men, all charged with first-degree murder, were arrested Thursday in central Virginia and are being held without bond after appearances Friday in D.C. Superior Court.

Spencer was ordered to undergo a psychiatric evaluation.

“Reggie said he had on a mask and knocked on Glenn’s door” in the 1300 block of Levis Street NE, the affidavit says. “Glenn eventually answered the door. Reggie said he pushed the door open and that he, Phillip and Terrell went inside.”

Spencer said Scarborough was gagged, duct-taped and stabbed, according to the affidavit. He “said that after choking Glenn, he wrapped the belt around Glenn’s neck and pulled it,” the affidavit says.

“But the belt broke.”