The suspect in Wednesday's deadly shooting at the University of Nevada, Las Vegas, was armed with more than 150 rounds of ammunition and used a handgun he legally purchased last year, authorities said Thursday.
The suspect -- a former college professor identified by police as Anthony Polito, 67 -- was killed in a shootout with responding officers about 10 minutes after shots were first reported at UNLV's Beam Hall, Las Vegas Metropolitan Police Department Sheriff Kevin McMahill said at a media briefing.
The suspect had pulled up to the campus with 11 magazines, and nine loaded magazines were found on his person, McMahill said. It is unclear how many rounds were fired, McMahill said. The suspect had a Taurus 9 mm handgun that was legally purchased last year, the sheriff said.
Three UNLV professors were killed. A fourth shooting victim -- a 38-year-old visiting professor -- was injured and hospitalized in life-threatening condition, McMahill said.
A motive remains under investigation. He is believed to have acted alone, McMahill said.
The sheriff said he believes the suspect was heading to the nearby student union before he was confronted by officers outside Beam Hall.
"I believe we averted a much larger tragedy by the actions of that heroic police officer," McMahill said.
The suspect lived in Henderson, Nevada, and previously worked as an assistant professor at East Carolina University. He had applied for jobs with several institutions of higher education in Nevada and "was denied each time," McMahill said.
He had applied for a college professorship at UNLV, but was not hired, sources told ABC News.
He was struggling financially and a notice of eviction was taped to his front door, McMahill said.
Prior to the shooting rampage, the suspect visited a post office in Henderson and sent 22 letters to university personnel across the U.S. with no return address, according to McMahill. All of the people who were sent letters were identified and contacted, McMahill said.
A law enforcement source with knowledge of the investigation told ABC News that authorities had all 22 envelopes in their possession, which they intercepted.
Preliminary test results on white powder found in the first envelope to be opened have come back as being talcum powder, the source said, The authorities have to test every envelope with care and while following procedure, which will take time.
While executing a search warrant at the suspect's home, authorities found a chair with an arrow pointing down to a document that was "similar to a last will and testament," McMahill said.
During the investigation, authorities also determined that Polito had a list of people "he was seeking" at UNLV and faculty from East Carolina University, McMahill said. None of the individuals on the target list were victims in the shooting, he said.
"We have contacted almost everyone on those lists to make sure that they are all right," McMahill said.
A law enforcement source told ABC News authorities they believe Polito spent a few minutes looking for people on the list, but was unsuccessful in finding them and then shot other victims who happened to be in the building.
Investigators are looking into the suspect's past employment. They are also scrubbing the suspect's social media, devices and computers they seized, but right now there were no warning signs from friends or family prior to the incident, authorities said.
As the investigation continues, UNLV's final exams, which were set for next week, have been canceled, university President Keith Whitfield announced Friday.
"Instead, we are providing flexibility for faculty and instructors -- as well as students -- to bring this semester to a positive end," Whitfield said.
He added, "Given the physical and emotional trauma that the university community has endured, and because of the impact to campus facilities, we have decided that faculty and staff should continue to work remotely through the end of the calendar year."
Suspect in UNLV shooting had more than 150 rounds of ammunition: Police originally appeared on abcnews.go.com