Police released a batch of 911 recordings Wednesday from the first two shootings in a wave of Phoenix serial killings earlier this year, hoping that the calls might revive an investigation that has generated few leads in recent months.
A female caller in one recording was crying as she reported on March 18 that her brother had been shot but that she did not see the shooter.
FULL COVERAGE: Serial street shootings plague Phoenix
A man living nearby said he was awakened by sound of the 11 or 12 gunshots and a vehicle speeding away. Other calls were about a shooting that happened one day earlier.
Authorities have received about 3,000 tips in the investigation into who is responsible for killing seven people and wounding two others in shootings from March until July.
But police say the number of tips has plummeted since the last attack.
Police spokesman Sgt. Jonathan Howard said investigators are confident the case will be solved by a tip from someone who knows a person involved in the attacks.
"We are doing everything we can, forensically," Howard said. "The information that will give us a break in this case will come from witness testimony in this community."
Police say the victims were attacked as they stood outside their homes or sat in vehicles after dark. They were fired upon by someone who was sitting in a car or had just stepped out of a vehicle. All but one of the killings has taken place in the city's Maryvale section, a predominantly Hispanic neighborhood Phoenix's west side.
Investigators believe the crimes were carried out by a lanky Hispanic man in his early 20s, but they are leaving open the possibility that someone else may have participated in the attacks. They don't believe the attacks are racially motivated. No motive has been established.
Nearly two months ago, authorities held a news conference to drum up public interest in the case and announce that the reward offered had been upped to $75,000.
The first shooting happened on March 17, when a Nissan drove past two teenagers, pulled a U-turn and a man inside the vehicle opened fire, hitting a 16-year-old boy in the arm, abdomen and hip. He survived the attack.
In one recording, a woman told a 911 operator that she heard eight shots fired, but didn't see a vehicle leaving the scene. In another call, a relative of the victim fielded questions from an operator as the relative headed to the scene of the shooting.
The second shooting happened the next day, on March 18, when a 21-year-old man was shot while standing in the street outside of his vehicle. He also survived.
In a recording, the victim's sister was upset and crying as told the operator that she did not see the shooter.
"They pulled up in front of our house and they shot him when he got out the car," she said.
Howard said investigators are continuing to analyze physical evidence recovered from the scenes and are now focusing on lower priority tips after having worked their way through tips that required more immediate attention.
They also are trying to find neighbors who might have security camera footage of the shootings and working with community groups to seek out useful information.
People living in the Maryvale neighborhood have said some immigrants who could have valuable information about the killer may be reluctant to come forward for fear of deportation.
Authorities have said witnesses or victims fearful about their immigration status should not be afraid to come forward, adding that that the police department accepts anonymous tips.
"It's difficult and challenging to change everyone's feelings," Howard said.