New York: Fears of another Virginia Tech-like massacre gripped St John's University when a student was arrested after he was spotted walking through the campus carrying a powerful .50 caliber rifle and wearing a Halloween mask.

The suspect, Omesh Hiraman, 22, an immigrant from Guyana, was arrested with the help of a police cadet and was being grilled by detectives on Wednesday night.

The loaded weapon, manufactured by Wolf, in Spain, carries just one shot, and while no other ammunition was found on Hiraman, police were searching his New York home for more bullets and for clues to what Hiram intended to do.

Turning heads

He was supposed to be in a business class at the time of his arrest, police said, but walked right past it and did little to remain unobtrusive.

The weapon, police said, was only partly concealed by a black plastic garbage bag, and his mask, which looks vaguely like Ronald Reagan or George W. Bush, turned heads as he walked through the campus.

"He was wearing a black hooded sweatshirt," said freshman Kimberly Forrest, 18. "I thought it was strange that a person was wearing a hoodie and a mask."

Christopher Benson, 21, thought the same thing.

Benson, a criminal justice major and NYPD cadet, says he was sitting on a bench in front of St John's Hall, talking on his cell phone to his girlfriend, Erin, when he "saw this person walk past me with a mask... and he was carrying what looked like a rifle."

Benson matter-of-factly told his girlfriend what he just saw and said he had to go. "Let me check this out," he remembers telling Erin.

Confronted

Then, keeping a distance of about 6 metres as he learned in his cadet training, Benson followed Hiraman, who was walking "very fast". About 45 seconds later, however, Hiraman turned a corner and was confronted by a security officer who grabbed the rifle.

But Hiraman wouldn't let it go, and Benson said he moved in, using his 6-foot-2-inch 115kg frame to overpower the 5-foot-11 inch, 60kg suspect. Hiraman let go of the gun, and Benson pinned him against the wall of Marillic Hall, aided by other campus security officers.

At that point, the school was locked down, all entrances and exits closed off as police conducted a building by building search.