On Wednesday, May 26, a mass shooting incident at a rail yard in San Jose, California claimed the lives of 10 people.

On the morning of the incident, a transit employee of the Santa Clara Valley Transportation Authority (VTA) identified as Samuel Cassidy, reportedly came to his workplace in downtown San Jose and opened fire, killing nine of his co-workers before turning his weapon on himself and taking his own life, NBC News reported.

Dallas Mayor Eric Johnson took to twitter to voice his support for the victims and their family.

“I am heartbroken by the horrific mass shooting today in San Jose,” Johnson Wrote in a May 26 Twitter post. “The victims and their loved ones, the people of San Jose, and my good friend Mayor @sliccardo are in my thoughts. Dallas stands with you all.” 

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Authorities say the victims were found in two separate buildings and that the suspect used two semi-automatic pistols and 11 magazines full of ammunition in the shooting.

“This is a horrific day for our city, and it is a tragic day for the VTA family, and our heart pains for the families and the co-workers because we know so many are feeling deeply this loss of their loved ones and their friends,” San Jose Mayor Sam Liccardo said in a statement, according to NBC News.

The suspect allegedly set fire to his home before going to his workplace, according to ABC 7 News. Investigators discovered Molotov cocktails, twelve firearms and over 20,000 rounds of ammunition in the damaged home. A search of the suspect’s locker at his workplace contained materials to that could be used to create explosives.

“It is clear that this was a planned event and the suspect was prepared to use his firearms to take as many lives as he possibly could had sheriff’s deputies not made entry to stop his rampage,” the department said, ABC 7 News reported.

The shooter’s motive for his deadly actions remains unclear, but officials say that he had a known history of dissatisfaction with his employer.

Cassidy’s ex-wife told ABC 7 News that he had talked about killing his co-workers over a decade ago.