The problems were almost immediate when Cristalina Warner moved in with her grandmother a year ago, Warner’s mother said. The University of Maryland graduate and former law school student was so beset with mental and other health problems that she had become openly “hateful and vicious” toward the 83-year-old family matriarch, her mother said.

Early Sunday morning, Prince George’s County police officers found Warner’s grandmother — Dorothy Ogden — fatally shot and wrapped in plastic and blankets in the living room of her Accokeek home, according to police charging documents. Homicide detectives think Warner, 32, killed the woman who was trying to take care of her over simple household disputes, police said.

“She loved my mother dearly, and things are so twisted in her mind,” said LouAnn Warner, Cristalina Warner’s mother and Ogden’s daughter. “It’s a horrible, horrible thing.”

Ogden’s slaying came during an exceptionally violent weekend in Prince George’s County. From Friday night through Sunday, five people were killed and seven others wounded in seven separate incidents, with motives that included robbery, drug disputes and domestic squabbles, police said. Prince George’s Police Chief Mark Magaw said that while none of the victims seemed to have been targeted at random, their slayings were of grave concern.

“This department never forgets that these numbers represent members of our community,” Magaw said.

The weekend violence began just before 10 p.m. Friday, when a gun battle erupted in a secluded area of a Landover apartment complex, police officials said.

Brandon Wiggins, 17, of Capitol Heights was killed and another person involved in the gunfight was wounded, said Assistant Prince George’s Police Chief Kevin Davis. He said the incident was “potentially a drug-related robbery or dispute.”

About 25 minutes later, gunfire erupted again in a Hyattsville area apartment complex, Davis said. This time, he said, three people were wounded in an apartment that seemed to double as a tattoo parlor. He said detectives had identified a suspect who had some type of dispute with the victims, and police were working to find him.

About 1:20 a.m. Saturday, another teen was killed. Police said Lester Amilcar Flores-Quintanilla, 19, and two others had just been denied entry to the Galaxy nightclub and were walking on Woodberry Street in Lewisdale when someone tried to rob them. Flores-Quintanilla, a member of the MS-13 gang, was shot and killed, police said, and the assailants remain at large.

“The main cause of that, we believe, is robbery,” Magaw said. “We’re looking at an overtone of a gang issue, but we’re still investigating.”

On Saturday, 25-year-old Ashley McClurkin was slain in her Suitland apartment. Her friend, Audrea Blackwell, 24, was charged with first-degree murder and related counts, accused of shooting McClurkin during an ongoing dispute. Blackwell also shot herself in the leg, police said, and was found about a mile from the apartment.

Tarel McClurkin, Ashley McClurkin’s uncle, declined to comment on the shooting but said his niece was “loved and cherished.”

“She’s a beloved family member and a spirited young woman whose life, honestly, was ended way too soon,” he said. “It never even got started.”

Police began investigating Ogden’s slaying later Saturday night, arriving at her Danville Road home after Cristalina Warner called 911, according to charging documents. Warner initially told officers that her grandmother was in the kitchen when she left the home about 7 p.m. Saturday and that she returned to find the side door open, according to the documents. She told the officers that although her grandmother’s car was in the driveway, she could not find the 83-year-old, her purse or her cellphone.

After an officer found Ogden’s body, Warner gave “a statement confessing to shooting and killing her grandmother,” the documents state. She was charged with first-degree murder, online court records show.

LouAnn Warner said her daughter was once a well-adjusted young woman. “Cristy,” as family members called her, graduated from the University of Maryland, where she studied government, and briefly pursued a law degree at Catholic University, her mother said.

“Very bright young lady,” she said.

About three years ago, though, something changed, LouAnn Warner said. Her daughter dropped out of law school and broke ties with her family, she said. She said she suspected her daughter was ill — possibly with Lyme disease and psychiatric issues — but Cristalina Warner kept most of her medical information private.

LouAnn Warner said that in January 2011, her daughter reached out to the family for help, saying she was sick. The family devised a plan for Cristalina Warner to move in with her grandmother a few months later, in hopes that “they would take care of each other.”

“But it didn’t end up a help at all, obviously,” LouAnn Warner said.

She said her daughter’s mental problems did not seem to improve at her grandmother’s. At times, LouAnn Warner said, Cristalina Warner would scrub the finish off silverware because she feared germs. LouAnn Warner said her mother — who volunteered as a cook for her church — became somewhat reclusive, spending time in her bedroom to avoid her granddaughter.

LouAnn Warner said she went to her mother’s house Saturday night, after a family friend told her that something might be amiss. Her daughter was there, she said, and seemed scared because she had returned to a house with an open door. Ogden was dead inside.

“My God, we were always so close — my mother, my daughter and myself,” LouAnn Warner said.

On Sunday morning, police said, 21-year-old David Shaw was fatally wounded in a District Heights home after he apparently tried to rob a group of six people he was hanging out with. After Shaw shot and wounded one in the group, police said, another person took his gun and shot him. Police said they are investigating the case as a “justified” homicide, although they have referred it to the state’s attorney’s office for review.

The weekend’s final shooting came about 11:30 a.m. Sunday in Hillcrest Heights. Police said two people shot a man during a robbery attempt, but the man was expected to survive.

Even with the weekend’s bout of violence, homicides are down significantly in Prince George’s this year. There have been 17 slayings and one apparently justified homicide in Prince George’s this year, compared with 27 killings and two cases deemed justified at the same time last year.

Staff researcher Jennifer Jenkins and staff writer Stefanie Dazio contributed to this report.