Two-year-old Aiden McCarthy lost both his parents in the Highland Park, Illinois shooting at the July 4th parade. 

A billionaire hedge fund manager, William (“Bill”) Ackman, donated $18,000 to a fundraising event on a GoFundMe page to help Aiden.

Ackman is the founder and Chief Executive Officer of Pershing Square Capital. His office confirmed to Fortune on Wednesday that he is the William Ackman who made the donation.

Ackman voiced his frustrations on Twitter in response to the Highland Park shooting.

“There have been 309 mass shootings in the US YTD, an average of 12 per week, nearly two per day. The trend is not our friend. Do we do anything differently when there are 50/week? 100? What about when there is one every hour and no community is safe? Should we change anything?” Ackman wrote.

The GoFundMe effort has already raised over $2.5 million for Aiden.  His parents, Kevin and Irina McCarthy were killed, along with five other people, when Robert Crimo III shot into the crowd from a rooftop at the July 4th parade with an AR-15-type rifle, in an affluent suburb outside Chicago. 

Aiden was found in the chaos by a spectator at the parade, on the ground beneath a wounded man. He was brought to a fire station by another couple, and was later sent to his grandparents.

Aiden’s grandparents said that Aiden’s father “shielded him from bullets with his body.”

A family friend created the GoFundMe page, hoping to raise money to help Aiden’s grandparents take care of him. 

The fundraiser has received donations from more than 40,000 people.