NIAGRA FALLS, New York (WTVO) — An Illinois mother was killed, and her 5-year-old son in critical condition, after the pair fell off a 90-foot cliff at Niagra Falls on Monday.

According to the State Parks Police Department, the 34-year-old woman climbed over a railing along with her son around 12:30 p.m. and fell to the bottom of the frozen gorge.

According to NBC Chicago, emergency workers tried to rescue the pair but were unable to save the woman. The boy was airlifted to a hospital in Buffalo, New York where he underwent surgery and remains in critical condition.

“We don’t believe this was an accident,” State Parks Police Capt. Chris Rosa said at a news conference on Tuesday.

The woman’s identity has not been released.