Keven Quiroz, 23, is accused of assaulting the man last Friday evening at Sierra Vista Middle School in an attack captured on video.
Investigators suspect the attack stemmed from a dispute over Quiroz letting his dog off leash, according to Sgt. Karie Davies with the Irvine Police Department. Davies said it does not appear the victim's ethnicity was a factor in the attack. The victim was walking his dog at the time.
Surveillance video and photos were released Monday, which led to the anonymous tip that identified Quiroz as a possible suspect, according to police.
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Investigators said the victim was trying to defend his dog from getting attacked by the unleashed dog.
When the victim was trying to defend his dog, investigators said, the suspect hit the older man in the back of the head. The victim left the scene with the dog and was later taken to a hospital for treatment.
Quiroz was arrested at his apartment in Tustin, where police say they recovered evidence linking him to the assault. He was booked on suspicion of assault with a deadly weapon and elder abuse, according to IPD.
An unloaded rifle in the suspect's vehicle was also found. Police say the weapon is unrelated to the case, but detectives are trying to determine if the suspect legally obtained it.
Irvine police initially described the suspect as a male in his late teens.
City News Service contributed to this report.