This article is part of an occasional series in the District Extra on unsolved homicides.

The mysterious person called detectives within a few weeks of the brutal killing of Darren L. Carter, a 21-year-old man found shot to death and burned last summer in a Northeast Washington alley.

The caller didn't leave a name or phone number but provided enough clues that investigators are convinced that he or she knows details about the killing. The caller is considered so crucial to the case that Detective Scott Gutherie, who is leading the investigation, won't even say whether the caller was a man or a woman.

"We would really like to hear from that person again," Gutherie said. "The person's help could bring a swift closure to this case. There is no doubt in my mind that this anonymous caller knows who committed this crime."

The killing occurred about 3 a.m. June 19. Carter's body was discovered by police officers on routine patrol responding to a report of a fire in an alley behind the 1200 block of Linden Place NE, just south of H Street NE. There, the officers found Carter burning next to a fence. An autopsy determined that he had been fatally shot, police said.

"I think it's safe to say it was overkill," Gutherie said. "Someone was determined to make sure he was dead."

It wasn't the first time somebody tried to kill Carter, police said.

Five days before the slaying, Carter was shot in the right leg. The shooting occurred a few blocks from where his body was later found.

Gutherie said police have developed no suspects in the first shooting or the killing, but they are investigating whether the two crimes are connected.

Carter's family said they have been struggling to understand why somebody would kill him. His mother, Terry Carter, said she often takes a bus to work that passes the crime scene. She can still see burn marks on the fence. "The bus seems to get stuck right there every time," the mother said. "I just sit there crying. I wish the bus would get going."

Darren Carter grew up in Southeast and Northeast Washington and attended Joel Elias Spingarn Senior High School, his mother said. He was arrested three times as a juvenile in stolen cars and was sent to the city's Oak Hill juvenile detention facility until he was 21, she added.

While there, he earned a general equivalency diploma, she said.

Carter was released in May, a month before he was killed, and had gotten a job on the cleaning staff of the D.C. Convention Center, his mother said.

His return from Oak Hill was emotional, his mother said. She was in the yard of her Northeast Washington home when someone told her that somebody in the kitchen wanted to see her.

"It was him," Terry Carter said. "I tackled him and hugged him. We fell to the ground. He was my son. He was my heart. . . . He comes to me in my dreams. He tells me everything is all right and that he knows who did this."

Anyone with information is urged to call D.C. police at 202-727-9099 or 202-645-7054. Police offer rewards of up to $25,000 for information leading to the arrest and conviction of a suspect in a homicide.

Police are still looking for the person who shot and killed Darren L. Carter.