A witness who was at Trinity Bellwoods Park when a man was fatally struck by a falling branch spoke out about giving the man CPR on Monday.

Mike Lee said he can’t stop thinking about the incident, calling it “senseless.”

He told CTV Toronto he heard the tree limb crack while he was enjoying a picnic with friends at the park last Friday. Lee said he ran over to help after he saw the branch fall onto the man.

Two other people also rushed to the man’s side to perform CPR until paramedics arrived, said Lee.

Emergency crews were unable to save the man’s life. Police said the man, believed to be in his 30s, was sitting under the tree with his pregnant wife. Police said the couple was in Toronto on a work visa.

A memorial of flowers and cards were placed at the base of the tree.

Toronto Mayor John Tory expressed his condolences to the victim’s family and said city officials are working to determine why this happened.

One theory that is being considered is summer branch drop, when seemingly healthy tree limbs snap off with rising temperatures. It has been seen in 19 different species of trees, including the Siberian elm.

Lee said he has started an online fundraising campaign to help the victim’s family. The goal is set at $20,000 and so far $415 has been raised.

Since the man’s death, city officials said parks staff have deemed the tree healthy.

The limb is now being examined at a city works yard.