Houston police say the man and his attacker had a confrontation on the sidewalk beneath the Pierce elevated freeway. Another man tried to help, but police say he was also stabbed.
The victims made it as far as the McDonald's parking lot near the sidewalk and collapsed.
According to onlookers, some witnesses ran after the suspect and held him for police.
It happened on a block of downtown Houston well known to both police and paramedics. The Houston fire department has responded more than 100 times this year to the area beneath the freeway and the downtown bus station.
The names of the victims and of the suspect have not been released. The survivor from the stabbing attack is said to be in serious condition.
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