Sixteen apparently random shootings that have killed three people and wounded two in the Phoenix area since June appear to be connected, police said Friday.
Authorities asked for the public's help in solving the crimes, which also included killings of dogs and horses.
"We have no motive, no witnesses, and that's the trouble," said police Cmdr. Kim Humphrey. "It's unfathomable that you could have 16 shootings and no one saw it or is talking about it."
Detectives said they had forensic evidence linking four shootings, but they would not give details. As for the other shootings, they said the timing and circumstances were too similar to be coincidence. Many took place overnight and appeared to target people out alone, Humphrey said.
Humphrey said the shooter was probably fairly skilled, because many shots were from a distance. A shotgun was used in two shootings, police said. They would not say what type of gun was used in the other attacks.
The shootings appear to have occurred in clusters and started in June, with others in July and August, followed by seven shootings on the night of Dec. 29-30.
In the December shootings, two homeless men were shot to death within a block of each other in central Phoenix, near another shooting that wounded a halfway-house resident. The three shootings were reported within a minute of each other.
A woman was wounded and some dogs were also shot nearby in a 3 1/2 -hour period that night.
The shootings were in Phoenix and in the suburbs of Tolleson and Avondale.