A UPS employee was arrested after he sent threatening texts to his employer indicating he was planning a mass shooting at their Silicon Valley workplace.
Thomas Andrews, 32, led the local authorities on a pursuit after refusing to pull over, eventually stopping in San Jose after The California Highway Patrol joined the Sunnyvale team.
He was booked for multiple offences, including driving under the influence, evading police and various counts of weapons violations according to the Sunnyvale Department of Public Safety.
The police then found more than 20,000 rounds of handgun and rifle ammunition, five tactical-style rifles and a shotgun when they searched Mr Andrews' residence.
Sunnyvale police Captain Dan Pistor told the Associated Press that his team's swift work helped minimise a situation that could have been very serious.
"Initially he indicated he wanted to fight with the officers, but then he surrendered without injury," Mr Pistor said.
"I definitely think we avoided a tragedy."
Investigators are attempting to found out how Mr Andrews' obtained the firearms at his residence.
Mr Pistor told the Associated press that Mr Andrews was upset with his employer but admitted the police were currently unsure as to why.
UPS told CNN that they are working with the authorities to help conduct their investigation.
Additional reporting by the AP
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