A pedestrian walks Wednesday along Branch Avenue near the intersection of Colebrook Road, where a man was fatally shot Tuesday in Prince Georges County. (Bonnie Jo Mount/WASHINGTON POST)

The fatal shootings of four people in Prince George’s County over a 48-hour spasm of violence have left families reeling with grief and renewed residents’ old fears about the safety of the D.C. suburb they call home.

In the latest incident, a 27-year-old Baltimore man pumping gas Tuesday night in Hillcrest Heights was killed by a stranger who investigators believe was high on PCP. That came hours after an 18-year-old freshman at Suitland High School and his friend were shot at an apartment complex in Forestville.

“It is just so devastating,” said Theresa Williams, the mother of Aaron Kidd, the student killed at the complex. “This should not have happened to any family.”

The anger and sadness were visible Wednesday night as more than 200 people, most of them teenagers, poured into a shopping center parking lot in Hillcrest Heights to commemorate Charles Walker Jr., a 15-year-old freshman at Suitland High School who was killed Monday. The site is about a block from where Walker was shot.

Some youths cried. Others shouted and shoved each other. The outbursts forced dozens of teenagers to scatter in fear of further violence, despite a bolstered police presence.

“We lost a good one out here. We lost a good soldier out here for no good . . . reason,” Lester Massey Jr., Walker’s uncle, told the crowd.

In an interview, Massey said that he spoke with his nephew shortly before the shooting and that Walker said he was happy. The teenager told Massey he had just bought a pair of Timberland boots for his girlfriend, the pair of shoes that led to a robbery and, authorities think, cost him his life.

The burst of mayhem brings the county’s homicide count to 15 this year, compared with 10 by this point in 2012. It also brings to six the number of Prince George’s County school students slain since the start of the current school year.

None of those slayings are believed to be connected, and no killing of a student is linked to another, police said. Still, the violence has sparked fears that crime might be ticking up in a county where 64 people were killed last year, a historic low.

“It’s just getting worse,” said Telita Plummer, 56, who on Wednesday was having her car worked on at the gas station where the Baltimore man was shot. The police are good, she said, “but it’s like it doesn’t matter.”

As nerve-rattling as the latest incident is, it does not mark the most severe spate of violence in recent years in Prince George’s. In January 2011, 15 people were killed, 12 of them in 11 days. Total violent crime is down nearly 17 percent compared with the same period last year, and overall crime is down 10 percent, according to police statistics.

Prince George’s Police Chief Mark A. Magaw said Wednesday that police are working tirelessly to quell the deadly violence.

“Nobody wants this,” he said. “Not our community, not this department.”

Williams last saw her son Tuesday morning, when she took him to breakfast at Chick-fil-A and then dropped him off at Suitland High School. Kidd, who was in the ninth grade because he has a learning disability and had recently returned to school after a year off — told her, “Mommy, I’ll see you later” before the two parted ways.

“I never saw him again,” Williams said.

Police said Kidd and Andre Walter Shuford, 18, were shot about 5:30 p.m. in the 3700 block of Donnell Drive. Shuford died Wednesday.

A woman who identified herself as Shuford’s mother would tell a reporter only that her son had gone to Forestville High School. Police have said the teenager had no connection with Prince George’s County schools at the time of his death.

Williams said that although she didn’t know Shuford well, he was friends with her son. Detectives do not know of a motive in the crimes.

Outside Suitland High School on Wednesday, some students said they were on edge.

“I’m not afraid. . . but I’m watching my back, looking over my shoulder,” said Anthony Coghill, 15, a sophomore. “Whether you know them or not, it takes a toll.”

Hours after the Forestville shooting, police said, officers were called to another startling incident in Hillcrest Heights: Eric Eugene Walker, 27, was gunned down by a stranger apparently high on PCP.

Walker, in the area with a friend from Baltimore, was pumping gas at the Open 24 Hours gas station near Branch Avenue and Colebrooke Drive when an armed stranger approached, police said. Police said that Walker ran across Branch Avenue and that the stranger, 34-year-old Duane Lamar Williams, shot him.

An off-duty D.C. police officer in plainclothes but carrying his service weapon came upon the scene and ordered Williams to drop his weapon. Williams tried to fire at him, but his gun malfunctioned and the off-duty officer did not fire back, police said.

County police officers soon arrived, saw Williams discard his gun between a few cars and moved to “swarm this guy and tackle him to the ground,” said Prince George’s Assistant Police Chief Kevin Davis. He said the officers first tried to use a stun gun on Williams, but possibly because of his suspected PCP use, there was no effect.

A woman who answered a phone number listed for Walker’s family members declined to comment, and efforts to reach Williams’s relatives were unsuccessful. Williams was charged with first-degree murder and related counts, police said.

Police also have made arrests in three of the six cases involving Prince George’s students. On Wednesday, they said they had charged five people with first-degree murder in the fatal shooting of Charles Walker Jr.

Police identified those charged as Derryck Antonio Green of Alexandria, 20; Jermani Maurice Whitner of Temple Hills, 18; Glenn Cornell Leach of the District, 23; Tayvon Delonte Williams of Oxon Hill, 21; and Kevin J. Smith of Temple Hills, 21.

All five were in a van that pulled alongside Walker on Monday as he walked down 28th Avenue carrying a bag of shoes, authorities said. They told the teen to give up the shoes, and when he tried to run, someone in the van shot him in the back, said a law enforcement official who spoke on the condition of anonymity because the investigation is continuing.

Maj. Michael Straughan, who commands the police’s criminal investigations division, said that Crime Solvers tips helped lead police to the suspects and that every suspect admitted “involvement” in the crime. He said police recovered the van used in the incident.

At Wednesday’s vigil, a cousin of Charles Walker Jr.’s blamed the teen’s death on “materialism.”

“These kids don’t realize that there are more important things out here,” Darlene Rainey said. “We want to get these kids and tell them to trust in God.”

Williams, Kidd’s mother, said she had spoken to her son about Walker’s death, and he told her he knew the boy in passing from school.

“Now,” she said, “I see what that other mother is going through.”

Williams said that while her son got into occasional trouble — he had recently been suspended, and court records show he was facing burglary charges — he was generally a “good kid” with no enemies. She said he loved playing basketball and dreamed of becoming a barber. His girlfriend is pregnant and is due in March, Williams said.

Hamil R. Harris, Jennifer Jenkins, Ovetta Wiggins and Clarence Williams contributed to this report.