LOS ANGELES, Feb. 21 (Xinhua) -- A 18-year-old student was arrested Wednesday for carrying gun to school Wednesday in Phoenix, the capital of Arizona. It was the fourth similar cases happened in the state in one week.

The local police department released a statement, saying Michael Helt was arrested before classes began at Liberty High School Wednesday morning after receiving an anonymous tip about Helt having a gun in his car while it was parked in the school's parking lot.

The KTAR news channel reported that the student told investigators that he accidentally brought the weapon to school and police confirmed that he did not make any threats to school or others.

It's the fourth similar case happened in Arizona in one week.

Last Thursday, Scottsdale police arrested 18-year-old student Justin Perotti on suspicion of carrying a weapon on school grounds after reports that he had a handgun in his vehicle parked at Chaparral High School.

At the same day, Phoenix police also arrested a 16-year-old student after he took a loaded handgun to Sierra Linda High School. The student said that he had the weapon for personal security and had no issues with anyone at school.

Parker High School 18-year-old student Daniel Aaker was arrested on Sunday after taking a shotgun on campus. He faced a charge of misconduct involving a weapon, though there was no indication he threatened anyone at the school.

Under Arizona law, an adult can have a firearm on school grounds if the person keeps the weapon in a locked vehicle, unloaded and not visible. Police said Aaker's shotgun, which was unloaded in his locked truck, was visible.

Tensions have been high on campuses in Arizona after a mass shooting at Marjory Stoneman Douglas High School in Parkland of Florida killed 17 people on Feb. 14.