(CNN) A Virginia Tech student was arrested Monday after police said he had an assault rifle and was trying to buy 5,000 rounds of ammunition.

Yunsong Zhao, 19, has been charged with illegal possession of an assault rifle while not being a US citizen, according to an arrest warrant obtained by CNN affiliate WSLS.

Police say Zhao had bought a former police vehicle -- which still had police markings -- and installed a special bumper to the car. The freshman student had also researched bulletproof vests, the document states.

Yungsong Zhao

Virginia Tech Police Chief Kevin Foust said Zhao was arrested without incident following a "lengthy investigation."

No more details about his arrest or the investigation have been released.

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