PHOENIX, Arizona (CNN) -- Police on Friday arrested two men they said were responsible for deadly shootings that have terrorized Phoenix, Arizona, for more than a year.

"These are the two monsters we've been hunting," Phoenix Mayor Phil Gordon told a news conference.

Officers detained Dale Hausner, 33, and Samuel John Dieteman, 30, at 11:30 p.m. Thursday at an apartment complex in Mesa, east of downtown Phoenix.

An officer was seen emerging from the apartment complex carrying two rifles wrapped in plastic bags.

Police said Hausner and Dieteman will face a lineup Friday afternoon and formal charges, including murder, are expected to follow. Police said they are certain Hausner and Dieteman are behind the "Serial Shooter" killings.

The "Serial Shooter" has been blamed by police in 36 shootings since May 2005. At least six people have been killed and 18 wounded. Horses and dogs also have been shot.

Still at large is the "Baseline Killer," responsible for a second serial killing spree blamed for 23 crimes, including robbery, sexual assault and eight murders.

Gordon told reporters: "We're not yet finished. I said last week that we had turned the tables on these criminals, that the hunters had become the hunted, and that Phoenix is a city on the offensive. No one should question that today."

Police believe no accomplices
Police said interviews were continuing with Hausner and Dieteman, both of whom have police records, said Phoenix Police Chief Jack Harris, who did not go into detail.

"We believe this is a pretty strong case," said Barnett Lotstein, a member of the Maricopa County Attorney's Office. "Police have substantial evidence."

Police suspect the two did not act in concert with others, said Assistant Phoenix Police Chief Kevin Robinson. Authorities may not know the motive for the shootings for some time, he said, adding that it appears all the victims were chosen at random.

The arrests followed information from a number of sources, Robinson said.

"It was not just calls from the public," he said. "It was work from all the law enforcement agencies."

He said the suspects are friends and were identified on Monday. On Thursday police tactical teams got an opportunity "to go in grab a hold of them," Robinson said.

Mesa police have linked the Sunday night killing of a 22-year-old woman, Robin Blasnek, to the "Serial Shooter" cases, citing forensic evidence.

Authorities have offered $100,000 rewards in each of the "Serial Shooter" and "Baseline Killer" cases.

Phoenix police have had about 200 officers working to try to solve the cases, the AP reports.