One of the emails noted that "There is nothing confirmed but it is suspected that a pellet gun might have been used in these incidents".
Since-deleted post from Twitter user describing shuttle attack. There are at least five Apple shuttles with significant damage, while nearby Greyhound bus services have not reported similar incidents, reports SFGate.
A police officer shouts for demonstrators to move out of the path of a Google shuttle bus in San Francisco in 2014.
Buses chartered by Silicon Valley tech giants like Google, Apple, and Facebook have sparked heated debates and protests in the past, with activists arguing that companies should be fined for picking up employees at city bus stops without paying taxes and disrupting San Francisco public transportation.
A source tells us that due to the nature of how the windows were impacted, some suspect the weapon being used could be a BB or pellet gun.
Some of the buses were headed north, others were headed south, but they all were hit on I-280 between state routes 84 and 85, a section of roadway that spans San Mateo and Santa Clara counties. Following the incidents, both the tech firms have rerouted employee buses keeping in mind the safety of their employees.
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Cited in SFGate's coverage, California Highway Patrol spokesman Art Montiel told that all attacks took place while the buses were occupied and travelling. "We received several reports of charter buses being damaged while driving on the I-280, but we're not sure what caused the damage".
The buses were not struck by accident, Montiel said.
The cracked windows did not injure anyone but Apple shifted shuttles to a longer route as a precaution.
At this point, it's unclear who is behind the attacks. "We're working closely with law enforcement to investigate these incidents", the email said, according to Mashable.
Apple and Google have yet to respond to NBC Bay Area's request for comment.
These shuttle buses have been targeted with vandalism before.