METRO police said the incident happened at about 1:40 p.m. on a Red Line train at the Preston Station downtown.
Police initially reported that an unknown individual had sprayed an unknown chemical substance, but later confirmed that the substance was mace. On Thursday, officials said the injuries of the three people who were hospitalized were non-life-threatening.
Passenger Daniel Ortiz said he didn't see anyone spray anything, but that a man began coughing shortly before the train pulled into the Preston Station.
"The guy next to me started coughing very, very loud," Ortiz said.
After that man exited the train, Ortiz said more people began to cough as the train continued to its next stop at the University of Houston-Downtown.
"People were banging on the windows to get people's attention from outside," Ortiz said.
"I just naturally put my face inside my shirt because I didn't know what was going on," he added.
METRO said passengers disembarked at the UHD station, but the person who sprayed the chemical wasn't apprehended. It remains unclear if he or she has been identified.
On Thursday, METRO officials said preliminary information indicates that the incident was not intentional, but a thorough investigation is ongoing.
The chemical incident comes almost two weeks after a man was fatally shot aboard a METRO bus on West Bellfort.
Elected leaders say it may be time for METRO to rethink security.
"They may need to put a bus monitor on some of their buses so that they will have a presence," Councilwoman Carolyn Evans-Shabazz said.
Passengers told Eyewitness News that the only METRO employees they usually see are the drivers themselves, who aren't armed.
"I don't want to put bus drivers in that position where they're gonna have to monitor and stop people because that could become confrontational," Evans-Shabazz said.
METRO said it's putting police officers on trains and buses, but did not specify if this would apply to METRO's entire fleet.
For the first time in decades, METRO said its officer ranks are fully staffed.
In October, METRO's website reported 1,279 major crimes aboard its trains and buses for the period from October 2023 to September 2024. But on Wednesday, METRO's website only shows 378 major crimes for the same period. A METRO spokesperson said the agency was looking into the discrepancy when Eyewitness News brought it to their attention.
You can read METRO's entire statement below:
"Safety remains our top priority, and we're taking concrete steps to enhance security across our transit system. As part of this commitment, we are putting officers back on board buses and trains to increase visibility, deter crime, and provide peace of mind for our customers and operators. We're proud of the work already underway by our new Police Chief. Chief Tien is working closely with the Houston Police Department and other law enforcement partners to strengthen coordination and improve response times system-wide.
For the first time in decades, we are now at full staffing for our full-time police officers. Under Chief Tiens' leadership, we're implementing a more strategic deployment plan that ensures officers are positioned where they are needed most, making our system safer and more responsive than ever before."
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