Detectives in Phoenix, Arizona, are checking hundreds of leads as they try to capture a serial killer who stalks victims while driving down darkened streets of poor, predominantly Latino neighbourhoods.
The killer, dubbed the Serial Street Shooter, has killed seven people and wounded two since March in nine attacks that have sown fear in Phoenix and led to a police plea for the public's help.
But the neighbourhood where six of the killings happened has many immigrants who are reluctant to come forward for fear of deportation.
The gunman strikes only after sunset and before dawn. All but one of the killings have taken place in the city's Maryvale section.
The victims include a 12-year-girl who was shot dead along with her mother and a friend of the mother.
The killer is described as a lanky Hispanic man in his twenties who either fires through an open window of his car or gets out to shoot from close range before driving off.
In the most recent attack, on July 11, a man and a four-year-old boy escaped injury after the gunman shot at a vehicle they were sitting in.
Investigators are checking hundreds of leads, trying to find out if neighbours or security cameras captured video footage of the killer.
They have put undercover officers on extra patrols and are receiving help from the FBI. And they are hoping someone who knows the shooter comes forward.
"He has someone he has talked to about this," Phoenix police spokesman Sergeant Jonathan Howard said. "This guy shot and killed a 12-year-old girl. We hope someone else's conscience catches up with them."
Experts on serial killers say that given the gunman's brazen outdoor attacks, he will make a mistake sooner or later - if he has not done so already.
Unlike other serial killers, who often stay in the shadows, this one has allowed witnesses to catch glimpses of him, enabling police to create a sketch they have circulated. Detectives also found shell casings at four crime scenes, though authorities will not say what ballistics revealed about the gun or guns used.
While Maryvale has a higher crime rate than many other Phoenix neighbourhoods, police statistics show it has been getting safer in the past decade.
But now some residents are staying inside after dark, abandoning a neighbourhood custom of sitting out on chairs in front gardens when the roasting summer heat dips below 100F.
Taking a break from painting the ranch-style home he is renovating, construction worker Marco Garcia said that he is watching for suspicious activity, but that the man police are looking for - young and Hispanic - would not stand out in Maryvale.
The cars the killer has used - described by witnesses as a late-1990s brown Nissan, a late-1990s black BMW and a white Cadillac or Lincoln - are like the vehicles many Maryvale drivers own, Mr Garcia said.
"Anyone who passes by here could be him," he said.
Another complicating factor is that many Maryvale residents are immigrants who are in the US illegally or do not have their paperwork in order and fear they will be deported if they go to police, said Maribel Diaz, with a neighbourhood watch group handing out fliers with the sketch of the gunman.
Those fears stem from Maricopa County Sheriff Joe Arpaio's heavy handed immigration enforcement and Arizona's tough anti-immigration laws, she said.
"It could be that someone saw something or looked at him or something but was scared and didn't report it," Ms Diaz said.
Authorities have been tight-lipped about the evidence they have, but DNA from the gunman would be almost impossible to recover from the crime scenes unless the shooter touched one of the victims or left behind an object, said Jack Levin, a criminologist at Northeastern University in Boston.
The first shooting happened on March 17, when the Nissan drove past three teenagers in Maryvale and pulled a U-turn. A police report said the driver was wearing a hat and fired a handgun, hitting a 16-year-old boy in the arm, abdomen and hip. He survived and described what he saw.
Diego Verdugo-Sanchez, 21, became the killer's first fatal victim on April 1, when he left his girlfriend's mother's home to lock his sport utility vehicle. He was hit three times in the torso and twice in the chest.
One witness claimed to have seen a person in the back seat of a car that left after the killing, leading police to warn that the shooter may have an accomplice.
Verdugo-Sanchez had a burglary conviction, and according to a police report, had used drugs in the past, giving rise to suspicions he was targeted because he had got mixed up in criminal activity, but police dismissed that possibility.
The deadliest attack came on June 12 when the suspect stopped his vehicle, got out and shot dead Angela Rochelle Liner, Stefanie Ellis, and Ellis' 12-year-old daughter Maleah as they sat in a parked car listening to music in front of a house. Ms Liner had 2,900 dollars with her but the suspect did not take it.
The serial killings are happening a decade after Phoenix was terrorised by the 2005-06 random shooting deaths of six people, with 19 more wounded. That case was solved when a drinking friend of the two killers informed on them.
The Serial Street Shooter may "get bolder and bolder", said Scott Bonn, a criminologist and sociology professor at Drew University in Madison, New Jersey. "But eventually he is going to make a mistake."